Reland "Sync requestFullscreen() and exitFullscreen() algorithms with the spec"

third_party/WebKit/Source/core/dom/Fullscreen.cpp

Index: third_party/WebKit/Source/core/dom/Fullscreen.cpp
diff --git a/third_party/WebKit/Source/core/dom/Fullscreen.cpp b/third_party/WebKit/Source/core/dom/Fullscreen.cpp
index f5d0797c9511f0ad501ad0659358d828cd1efae8..2b7200658fd9f9944efb788e3f256d6fea6e9e5a 100644
--- a/third_party/WebKit/Source/core/dom/Fullscreen.cpp
+++ b/third_party/WebKit/Source/core/dom/Fullscreen.cpp
@@ -162,17 +162,26 @@ bool FullscreenElementReady(const Element& element) {
   return true;
 }
 
-bool IsPrefixed(const AtomicString& type) {
-  return type == EventTypeNames::webkitfullscreenchange ||
-         type == EventTypeNames::webkitfullscreenerror;
-}
+// https://fullscreen.spec.whatwg.org/#dom-element-requestfullscreen step 4:
+bool RequestFullscreenConditionsMet(Element& pending, Document& document) {
+  // |pending|'s namespace is the HTML namespace or |pending| is an SVG svg or
+  // MathML math element. Note: MathML is not supported.
+  if (!pending.IsHTMLElement() && !isSVGSVGElement(pending))
+    return false;
 
-Event* CreateEvent(const AtomicString& type, EventTarget& target) {
-  EventInit initializer;
-  initializer.setBubbles(IsPrefixed(type));
-  Event* event = Event::Create(type, initializer);
-  event->SetTarget(&target);
-  return event;
+  // The fullscreen element ready check for |pending| returns false.
+  if (!FullscreenElementReady(pending))
+    return false;
+
+  // Fullscreen is supported.
+  if (!FullscreenIsSupported(document))
+    return false;
+
+  // This algorithm is allowed to request fullscreen.
+  if (!AllowedToRequestFullscreen(document))
+    return false;
+
+  return true;
 }
 
 // Walks the frame tree and returns the first local ancestor frame, if any.
@@ -191,7 +200,7 @@ Document* NextLocalAncestor(Document& document) {
   LocalFrame* frame = document.GetFrame();
   if (!frame)
     return nullptr;
-  LocalFrame* next = NextLocalAncestor(*document.GetFrame());
+  LocalFrame* next = NextLocalAncestor(*frame);
   if (!next)
     return nullptr;
   DCHECK(next->GetDocument());
@@ -209,34 +218,94 @@ Document& TopmostLocalAncestor(Document& document) {
   return document;
 }
 
-// Helper to find the browsing context container in |doc| that embeds the
-// |descendant| Document, possibly through multiple levels of nesting.  This
-// works even in OOPIF scenarios like A-B-A, where there may be remote frames
-// in between |doc| and |descendant|.
-HTMLFrameOwnerElement* FindContainerForDescendant(const Document& doc,
-                                                  const Document& descendant) {
-  Frame* frame = descendant.GetFrame();
-  while (frame->Tree().Parent() != doc.GetFrame())
-    frame = frame->Tree().Parent();
-  return ToHTMLFrameOwnerElement(frame->Owner());
+// https://fullscreen.spec.whatwg.org/#collect-documents-to-unfullscreen
+HeapVector<Member<Document>> CollectDocumentsToUnfullscreen(
+    Document& doc,
+    Fullscreen::ExitType exit_type) {
+  DCHECK(Fullscreen::FullscreenElementFrom(doc));
+
+  // 1. If |doc|'s top layer consists of more than a single element that has
+  // its fullscreen flag set, return the empty set.
+  // TODO(foolip): See TODO in |fullyExitFullscreen()|.
+  if (exit_type != Fullscreen::ExitType::kFully &&
+      Fullscreen::FullscreenElementStackSizeFrom(doc) > 1)
+    return HeapVector<Member<Document>>();
+
+  // 2. Let |docs| be an ordered set consisting of |doc|.
+  HeapVector<Member<Document>> docs;
+  docs.push_back(&doc);
+
+  // 3. While |docs|'s last document ...
+  //
+  // OOPIF: Skip over remote frames, assuming that they have exactly one element
+  // in their fullscreen element stacks, thereby erring on the side of exiting
+  // fullscreen. TODO(alexmos): Deal with nested fullscreen cases, see
+  // https://crbug.com/617369.
+  for (Document* document = NextLocalAncestor(doc); document;
+       document = NextLocalAncestor(*document)) {
+    // ... has a browsing context container whose node document's top layer
+    // consists of a single element that has its fullscreen flag set and does
+    // not have its iframe fullscreen flag set (if any), append that node
+    // document to |docs|.
+    // TODO(foolip): Support the iframe fullscreen flag.
+    // https://crbug.com/644695
+    if (Fullscreen::FullscreenElementStackSizeFrom(*document) == 1)
+      docs.push_back(document);
+    else
+      break;
+  }
+
+  // 4. Return |docs|.
+  return docs;
 }
 
-// Fullscreen status affects scroll paint properties through
-// LocalFrameView::userInputScrollable().
-void SetNeedsPaintPropertyUpdate(Document* document) {
-  if (!RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled() ||
-      RuntimeEnabledFeatures::rootLayerScrollingEnabled())
-    return;
+// Creates a non-bubbling event with |document| as its target.
+Event* CreateEvent(const AtomicString& type, Document& document) {
+  DCHECK(type == EventTypeNames::fullscreenchange ||
+         type == EventTypeNames::fullscreenerror);
 
-  if (!document)
-    return;
+  Event* event = Event::Create(type);
+  event->SetTarget(&document);
+  return event;
+}
 
-  LocalFrame* frame = document->GetFrame();
-  if (!frame)
-    return;
+// Creates a bubbling event with |element| as its target. If |element| is not
+// connected to |document|, then |document| is used as the target instead.
+Event* CreatePrefixedEvent(const AtomicString& type,
+                           Element& element,
+                           Document& document) {
+  DCHECK(type == EventTypeNames::webkitfullscreenchange ||
+         type == EventTypeNames::webkitfullscreenerror);
+
+  Event* event = Event::CreateBubble(type);
+  if (element.isConnected() && element.GetDocument() == document)
+    event->SetTarget(&element);
+  else
+    event->SetTarget(&document);
+  return event;
+}
 
-  if (LocalFrameView* frame_view = frame->View())
-    frame_view->SetNeedsPaintPropertyUpdate();
+Event* CreateChangeEvent(Document& document,
+                         Element& element,
+                         Fullscreen::RequestType request_type) {
+  if (request_type == Fullscreen::RequestType::kUnprefixed)
+    return CreateEvent(EventTypeNames::fullscreenchange, document);
+  return CreatePrefixedEvent(EventTypeNames::webkitfullscreenchange, element,
+                             document);
+}
+
+Event* CreateErrorEvent(Document& document,
+                        Element& element,
+                        Fullscreen::RequestType request_type) {
+  if (request_type == Fullscreen::RequestType::kUnprefixed)
+    return CreateEvent(EventTypeNames::fullscreenerror, document);
+  return CreatePrefixedEvent(EventTypeNames::webkitfullscreenerror, element,
+                             document);
+}
+
+void DispatchEvents(const HeapVector<Member<Event>>& events) {
+  for (Event* event : events)
+    event->target()->DispatchEvent(event);
 }
 
 }  // anonymous namespace
@@ -266,6 +335,12 @@ Element* Fullscreen::FullscreenElementFrom(Document& document) {
   return nullptr;
 }
 
+size_t Fullscreen::FullscreenElementStackSizeFrom(Document& document) {
+  if (Fullscreen* found = FromIfExists(document))
+    return found->fullscreen_element_stack_.size();
+  return 0;
+}
+
 Element* Fullscreen::FullscreenElementForBindingFrom(TreeScope& scope) {
   Element* element = FullscreenElementFrom(scope.GetDocument());
   if (!element || !RuntimeEnabledFeatures::fullscreenUnprefixedEnabled())
@@ -287,28 +362,6 @@ Element* Fullscreen::FullscreenElementForBindingFrom(TreeScope& scope) {
   return scope.AdjustedElement(*element);
 }
 
-Element* Fullscreen::CurrentFullScreenElementFrom(Document& document) {
-  if (Fullscreen* found = FromIfExists(document))
-    return found->CurrentFullScreenElement();
-  return nullptr;
-}
-
-Element* Fullscreen::CurrentFullScreenElementForBindingFrom(
-    Document& document) {
-  Element* element = CurrentFullScreenElementFrom(document);
-  if (!element || !RuntimeEnabledFeatures::fullscreenUnprefixedEnabled())
-    return element;
-
-  // For Shadow DOM V0 compatibility: We allow returning an element in V0 shadow
-  // tree, even though it leaks the Shadow DOM.
-  if (element->IsInV0ShadowTree()) {
-    UseCounter::Count(document,
-                      UseCounter::kDocumentFullscreenElementInV0Shadow);
-    return element;
-  }
-  return document.AdjustedElement(*element);
-}
-
 bool Fullscreen::IsInFullscreenElementStack(const Element& element) {
   const Fullscreen* found = FromIfExists(element.GetDocument());
   if (!found)
@@ -323,42 +376,40 @@ bool Fullscreen::IsInFullscreenElementStack(const Element& element) {
 Fullscreen::Fullscreen(Document& document)
     : Supplement<Document>(document),
       ContextLifecycleObserver(&document),
-      full_screen_layout_object_(nullptr),
-      event_queue_timer_(
-          TaskRunnerHelper::Get(TaskType::kUnthrottled, &document),
-          this,
-          &Fullscreen::EventQueueTimerFired),
-      for_cross_process_descendant_(false) {
+      full_screen_layout_object_(nullptr) {
   document.SetHasFullscreenSupplement();
 }
 
 Fullscreen::~Fullscreen() {}
 
-inline Document* Fullscreen::GetDocument() {
+Document* Fullscreen::GetDocument() {
   return ToDocument(LifecycleContext());
 }
 
 void Fullscreen::ContextDestroyed(ExecutionContext*) {
-  event_queue_.clear();
-
   if (full_screen_layout_object_)
     full_screen_layout_object_->Destroy();
 
-  current_full_screen_element_ = nullptr;
+  pending_requests_.clear();
   fullscreen_element_stack_.clear();
 }
 
 // https://fullscreen.spec.whatwg.org/#dom-element-requestfullscreen
-void Fullscreen::RequestFullscreen(Element& element) {
+void Fullscreen::RequestFullscreen(Element& pending) {
   // TODO(foolip): Make RequestType::Unprefixed the default when the unprefixed
   // API is enabled. https://crbug.com/383813
-  RequestFullscreen(element, RequestType::kPrefixed, false);
+  RequestFullscreen(pending, RequestType::kPrefixed);
 }
 
-void Fullscreen::RequestFullscreen(Element& element,
-                                   RequestType request_type,
-                                   bool for_cross_process_descendant) {
-  Document& document = element.GetDocument();
+void Fullscreen::RequestFullscreen(Element& pending, RequestType request_type) {
+  Document& document = pending.GetDocument();
+
+  // Ignore this call if the document is not in a live frame.
+  if (!document.IsActive() || !document.GetFrame())
+    return;
+
+  bool for_cross_process_descendant =
+      request_type == RequestType::kPrefixedForCrossProcessDescendant;
 
   // Use counters only need to be incremented in the process of the actual
   // fullscreen element.
@@ -372,379 +423,356 @@ void Fullscreen::RequestFullscreen(Element& element,
     }
   }
 
-  // Ignore this call if the document is not in a live frame.
-  if (!document.IsActive() || !document.GetFrame())
-    return;
+  // 1. Let |pending| be the context object.
 
-  // If |element| is on top of |doc|'s fullscreen element stack, terminate these
-  // substeps.
-  if (&element == FullscreenElementFrom(document))
-    return;
+  // 2. Let |error| be false.
+  bool error = false;
 
-  do {
-    // 1. If any of the following conditions are false, then terminate these
-    // steps and queue a task to fire an event named fullscreenerror with its
-    // bubbles attribute set to true on the context object's node document:
+  // 3. Let |promise| be a new promise.
+  // TODO(foolip): Promises. https://crbug.com/644637
 
-    // |element|'s namespace is the HTML namespace or |element| is an SVG
-    // svg or MathML math element.
-    // Note: MathML is not supported.
-    if (!element.IsHTMLElement() && !isSVGSVGElement(element))
-      break;
+  // 4. If any of the following conditions are false, then set |error| to true:
+  //
+  // OOPIF: If |requestFullscreen()| was already called in a descendant frame
+  // and passed the checks, do not check again here.
+  if (!for_cross_process_descendant &&
+      !RequestFullscreenConditionsMet(pending, document))
+    error = true;
+
+  // 5. Return |promise|, and run the remaining steps in parallel.
+  // TODO(foolip): Promises. https://crbug.com/644637
+
+  // 6. If |error| is false: Resize pending's top-level browsing context's
+  // document's viewport's dimensions to match the dimensions of the screen of
+  // the output device. Optionally display a message how the end user can
+  // revert this.
+  if (!error) {
+    if (From(document).pending_requests_.size()) {
+      UseCounter::Count(document,
+                        UseCounter::kFullscreenRequestWithPendingElement);
+    }
 
     // TODO(foolip): In order to reinstate the hierarchy restrictions in the
     // spec, something has to prevent dialog elements from moving within top
     // layer. Either disallowing fullscreen for dialog elements entirely or just
     // preventing dialog elements from simultaneously being fullscreen and modal
     // are good candidates. See https://github.com/whatwg/fullscreen/pull/91
-    if (isHTMLDialogElement(element)) {
+    if (isHTMLDialogElement(pending)) {
       UseCounter::Count(document,
                         UseCounter::kRequestFullscreenForDialogElement);
-      if (element.IsInTopLayer()) {
+      if (pending.IsInTopLayer()) {
         UseCounter::Count(
             document, UseCounter::kRequestFullscreenForDialogElementInTopLayer);
       }
     }
 
-    // The fullscreen element ready check for |element| returns true.
-    if (!FullscreenElementReady(element))
-      break;
-
-    // Fullscreen is supported.
-    if (!FullscreenIsSupported(document))
-      break;
-
-    // This algorithm is allowed to request fullscreen.
-    // OOPIF: If |forCrossProcessDescendant| is true, requestFullscreen was
-    // already called on a descendant element in another process, and
-    // getting here means that it was already allowed to request fullscreen.
-    if (!for_cross_process_descendant && !AllowedToRequestFullscreen(document))
-      break;
-
-    // 2. Let doc be element's node document. (i.e. "this")
-
-    // 3. Let docs be all doc's ancestor browsing context's documents (if any)
-    // and doc.
-    //
-    // For OOPIF scenarios, |docs| will only contain documents for local
-    // ancestors, and remote ancestors will be processed in their
-    // respective processes.  This preserves the spec's event firing order
-    // for local ancestors, but not for remote ancestors.  However, that
-    // difference shouldn't be observable in practice: a fullscreenchange
-    // event handler would need to postMessage a frame in another renderer
-    // process, where the message should be queued up and processed after
-    // the IPC that dispatches fullscreenchange.
-    HeapDeque<Member<Document>> docs;
-    for (Document* doc = &document; doc; doc = NextLocalAncestor(*doc))
-      docs.push_front(doc);
-
-    // 4. For each document in docs, run these substeps:
-    HeapDeque<Member<Document>>::iterator current = docs.begin(),
-                                          following = docs.begin();
-
-    do {
-      ++following;
-
-      // 1. Let following document be the document after document in docs, or
-      // null if there is no such document.
-      Document* current_doc = *current;
-      Document* following_doc = following != docs.end() ? *following : nullptr;
-
-      // 2. If following document is null, push context object on document's
-      // fullscreen element stack, and queue a task to fire an event named
-      // fullscreenchange with its bubbles attribute set to true on the
-      // document.
-      if (!following_doc) {
-        From(*current_doc).PushFullscreenElementStack(element, request_type);
-        From(document).EnqueueChangeEvent(*current_doc, request_type);
-        continue;
-      }
-
-      // 3. Otherwise, if document's fullscreen element stack is either empty or
-      // its top element is not following document's browsing context container,
-      Element* top_element = FullscreenElementFrom(*current_doc);
-      HTMLFrameOwnerElement* following_owner =
-          FindContainerForDescendant(*current_doc, *following_doc);
-      if (!top_element || top_element != following_owner) {
-        // ...push following document's browsing context container on document's
-        // fullscreen element stack, and queue a task to fire an event named
-        // fullscreenchange with its bubbles attribute set to true on document.
-        From(*current_doc)
-            .PushFullscreenElementStack(*following_owner, request_type);
-        From(document).EnqueueChangeEvent(*current_doc, request_type);
-        continue;
-      }
-
-      // 4. Otherwise, do nothing for this document. It stays the same.
-    } while (++current != docs.end());
-
-    From(document).for_cross_process_descendant_ = for_cross_process_descendant;
-
-    // 5. Return, and run the remaining steps asynchronously.
-    // 6. Optionally, perform some animation.
-    if (From(document).pending_fullscreen_element_) {
-      UseCounter::Count(document,
-                        UseCounter::kFullscreenRequestWithPendingElement);
-    }
-    From(document).pending_fullscreen_element_ = &element;
-    document.GetFrame()->GetChromeClient().EnterFullscreen(
-        *document.GetFrame());
-
-    // 7. Optionally, display a message indicating how the user can exit
-    // displaying the context object fullscreen.
-    return;
-  } while (false);
-
-  From(document).EnqueueErrorEvent(element, request_type);
+    From(document).pending_requests_.push_back(
+        std::make_pair(&pending, request_type));
+    LocalFrame& frame = *document.GetFrame();
+    frame.GetChromeClient().EnterFullscreen(frame);
+  } else {
+    EnqueueTaskForRequest(document, pending, request_type, true);
+  }
 }
 
-// https://fullscreen.spec.whatwg.org/#fully-exit-fullscreen
-void Fullscreen::FullyExitFullscreen(Document& document) {
-  // To fully exit fullscreen, run these steps:
-
-  // 1. Let |doc| be the top-level browsing context's document.
-  //
-  // Since the top-level browsing context's document might be unavailable in
-  // OOPIF scenarios (i.e., when the top frame is remote), this actually uses
-  // the Document of the topmost local ancestor frame.  Without OOPIF, this
-  // will be the top frame's document.  With OOPIF, each renderer process for
-  // the current page will separately call fullyExitFullscreen to cover all
-  // local frames in each process.
-  Document& doc = TopmostLocalAncestor(document);
-
-  // 2. If |doc|'s fullscreen element stack is empty, terminate these steps.
-  if (!FullscreenElementFrom(doc))
+void Fullscreen::DidEnterFullscreen() {
+  if (!GetDocument())
     return;
 
-  // 3. Remove elements from |doc|'s fullscreen element stack until only the top
-  // element is left.
-  size_t stack_size = From(doc).fullscreen_element_stack_.size();
-  From(doc).fullscreen_element_stack_.erase(0, stack_size - 1);
-  DCHECK_EQ(From(doc).fullscreen_element_stack_.size(), 1u);
-
-  // 4. Act as if the exitFullscreen() method was invoked on |doc|.
-  ExitFullscreen(doc);
+  ElementStack requests;
+  requests.swap(pending_requests_);
+  for (const ElementStackEntry& request : requests) {
+    EnqueueTaskForRequest(*GetDocument(), *request.first, request.second,
+                          false);
+  }
 }
 
-// https://fullscreen.spec.whatwg.org/#exit-fullscreen
-void Fullscreen::ExitFullscreen(Document& document) {
-  // The exitFullscreen() method must run these steps:
+void Fullscreen::EnqueueTaskForRequest(Document& document,
+                                       Element& pending,
+                                       RequestType request_type,
+                                       bool error) {
+  // 7. As part of the next animation frame task, run these substeps:
+  document.EnqueueAnimationFrameTask(
+      WTF::Bind(&RunTaskForRequest, WrapPersistent(&document),
+                WrapPersistent(&pending), request_type, error));
+}
 
-  // Ignore this call if the document is not in a live frame.
-  if (!document.IsActive() || !document.GetFrame())
+void Fullscreen::RunTaskForRequest(Document* document,
+                                   Element* element,
+                                   RequestType request_type,
+                                   bool error) {
+  DCHECK(document);
+  DCHECK(document->IsActive());
+  DCHECK(document->GetFrame());
+  DCHECK(element);
+
+  Document& pending_doc = *document;
+  Element& pending = *element;
+
+  // TODO(foolip): Spec something like: If |pending|'s node document is not
+  // |pendingDoc|, then set |error| to true.
+  // https://github.com/whatwg/fullscreen/issues/33
+  if (pending.GetDocument() != pending_doc)
+    error = true;
+
+  // 7.1. If either |error| is true or the fullscreen element ready check for
+  // |pending| returns false, fire an event named fullscreenerror on
+  // |pending|'s node document, reject |promise| with a TypeError exception,
+  // and terminate these steps.
+  // TODO(foolip): Promises. https://crbug.com/644637
+  if (error || !FullscreenElementReady(pending)) {
+    Event* event = CreateErrorEvent(pending_doc, pending, request_type);
+    event->target()->DispatchEvent(event);
     return;
+  }
 
-  // 1. Let doc be the context object. (i.e. "this")
-  // 2. If doc's fullscreen element stack is empty, terminate these steps.
-  if (!FullscreenElementFrom(document))
-    return;
+  // 7.2. Let |fullscreenElements| be an ordered set initially consisting of
+  // |pending|.
+  HeapDeque<Member<Element>> fullscreen_elements;
+  fullscreen_elements.push_back(pending);
 
-  // 3. Let descendants be all the doc's descendant browsing context's documents
-  // with a non-empty fullscreen element stack (if any), ordered so that the
-  // child of the doc is last and the document furthest away from the doc is
-  // first.
-  HeapDeque<Member<Document>> descendants;
-  for (Frame* descendant = document.GetFrame()->Tree().TraverseNext();
-       descendant; descendant = descendant->Tree().TraverseNext()) {
-    if (!descendant->IsLocalFrame())
+  // 7.3. While the first element in |fullscreenElements| is in a nested
+  // browsing context, prepend its browsing context container to
+  // |fullscreenElements|.
+  //
+  // OOPIF: |fullscreenElements| will only contain elements for local ancestors,
+  // and remote ancestors will be processed in their respective processes. This
+  // preserves the spec's event firing order for local ancestors, but not for
+  // remote ancestors. However, that difference shouldn't be observable in
+  // practice: a fullscreenchange event handler would need to postMessage a
+  // frame in another renderer process, where the message should be queued up
+  // and processed after the IPC that dispatches fullscreenchange.
+  for (Frame* frame = pending.GetDocument().GetFrame(); frame;
+       frame = frame->Tree().Parent()) {
+    if (!frame->Owner() || !frame->Owner()->IsLocal())
       continue;
-    DCHECK(ToLocalFrame(descendant)->GetDocument());
-    if (FullscreenElementFrom(*ToLocalFrame(descendant)->GetDocument()))
-      descendants.push_front(ToLocalFrame(descendant)->GetDocument());
+    Element* element = ToHTMLFrameOwnerElement(frame->Owner());
+    fullscreen_elements.push_front(element);
   }
 
-  // 4. For each descendant in descendants, empty descendant's fullscreen
-  // element stack, and queue a task to fire an event named fullscreenchange
-  // with its bubbles attribute set to true on descendant.
-  for (auto& descendant : descendants) {
-    DCHECK(descendant);
-    RequestType request_type =
-        From(*descendant).fullscreen_element_stack_.back().second;
-    From(*descendant).ClearFullscreenElementStack();
-    From(document).EnqueueChangeEvent(*descendant, request_type);
-  }
+  // 7.4. Let |eventDocs| be an empty list.
+  // Note: For prefixed requests, the event target is an element, so instead
+  // let |events| be a list of events to dispatch.
+  HeapVector<Member<Event>> events;
 
-  // 5. While doc is not null, run these substeps:
-  Element* new_top = nullptr;
-  for (Document* current_doc = &document; current_doc;) {
-    RequestType request_type =
-        From(*current_doc).fullscreen_element_stack_.back().second;
-
-    // 1. Pop the top element of doc's fullscreen element stack.
-    From(*current_doc).PopFullscreenElementStack();
-
-    //    If doc's fullscreen element stack is non-empty and the element now at
-    //    the top is either not in a document or its node document is not doc,
-    //    repeat this substep.
-    new_top = FullscreenElementFrom(*current_doc);
-    if (new_top &&
-        (!new_top->isConnected() || new_top->GetDocument() != current_doc))
-      continue;
+  // 7.5. For each |element| in |fullscreenElements|, in order, run these
+  // subsubsteps:
+  for (Element* element : fullscreen_elements) {
+    // 7.5.1. Let |doc| be |element|'s node document.
+    Document& doc = element->GetDocument();
 
-    // 2. Queue a task to fire an event named fullscreenchange with its bubbles
-    // attribute set to true on doc.
-    From(document).EnqueueChangeEvent(*current_doc, request_type);
-
-    // 3. If doc's fullscreen element stack is empty and doc's browsing context
-    // has a browsing context container, set doc to that browsing context
-    // container's node document.
-    //
-    // OOPIF: If browsing context container's document is in another
-    // process, keep moving up the ancestor chain and looking for a
-    // browsing context container with a local document.
-    // TODO(alexmos): Deal with nested fullscreen cases, see
-    // https://crbug.com/617369.
-    if (!new_top) {
-      current_doc = NextLocalAncestor(*current_doc);
+    // 7.5.2. If |element| is |doc|'s fullscreen element, terminate these
+    // subsubsteps.
+    if (element == FullscreenElementFrom(doc))
       continue;
-    }
 
-    // 4. Otherwise, set doc to null.
-    current_doc = nullptr;
-  }
+    // 7.5.3. Otherwise, append |doc| to |eventDocs|.
+    events.push_back(CreateChangeEvent(doc, *element, request_type));
 
-  // 6. Return, and run the remaining steps asynchronously.
-  // 7. Optionally, perform some animation.
+    // 7.5.4. If |element| is |pending| and |pending| is an iframe element,
+    // set |element|'s iframe fullscreen flag.
+    // TODO(foolip): Support the iframe fullscreen flag.
+    // https://crbug.com/644695
 
-  // Only exit fullscreen mode if the fullscreen element stack is empty.
-  if (!new_top) {
-    document.GetFrame()->GetChromeClient().ExitFullscreen(*document.GetFrame());
-    return;
+    // 7.5.5. Fullscreen |element| within |doc|.
+    // TODO(foolip): Merge fullscreen element stack into top layer.
+    // https://crbug.com/627790
+    From(doc).PushFullscreenElementStack(*element, request_type);
   }
 
-  // Otherwise, enter fullscreen for the fullscreen element stack's top element.
-  From(document).pending_fullscreen_element_ = new_top;
-  From(document).DidEnterFullscreen();
-}
+  // 7.6. For each |doc| in |eventDocs|, in order, fire an event named
+  // fullscreenchange on |doc|.
+  DispatchEvents(events);
 
-// https://fullscreen.spec.whatwg.org/#dom-document-fullscreenenabled
-bool Fullscreen::FullscreenEnabled(Document& document) {
-  // The fullscreenEnabled attribute's getter must return true if the context
-  // object is allowed to use the feature indicated by attribute name
-  // allowfullscreen and fullscreen is supported, and false otherwise.
-  return AllowedToUseFullscreen(document.GetFrame()) &&
-         FullscreenIsSupported(document);
+  // 7.7. Fulfill |promise| with undefined.
+  // TODO(foolip): Promises. https://crbug.com/644637
 }
 
-void Fullscreen::DidEnterFullscreen() {
-  if (!GetDocument()->IsActive() || !GetDocument()->GetFrame())
-    return;
+// https://fullscreen.spec.whatwg.org/#fully-exit-fullscreen
+void Fullscreen::FullyExitFullscreen(Document& document) {
+  // 1. If |document|'s fullscreen element is null, terminate these steps.
 
-  // Start the timer for events enqueued by |requestFullscreen()|. The hover
-  // state update is scheduled first so that it's done when the events fire.
-  GetDocument()->GetFrame()->GetEventHandler().ScheduleHoverStateUpdate();
-  event_queue_timer_.StartOneShot(0, BLINK_FROM_HERE);
+  // 2. Unfullscreen elements whose fullscreen flag is set, within
+  // |document|'s top layer, except for |document|'s fullscreen element.
 
-  Element* element = pending_fullscreen_element_.Release();
-  if (!element)
-    return;
+  // 3. Exit fullscreen |document|.
 
-  if (current_full_screen_element_ == element)
-    return;
+  // TODO(foolip): Change the spec. To remove elements from |document|'s top
+  // layer as in step 2 could leave descendant frames in fullscreen. It may work
+  // to give the "exit fullscreen" algorithm a |fully| flag that's used in the
+  // animation frame task after exit. Here, retain the old behavior of fully
+  // exiting fullscreen for the topmost local ancestor:
+  ExitFullscreen(TopmostLocalAncestor(document), ExitType::kFully);
+}
 
-  if (!element->isConnected() || &element->GetDocument() != GetDocument()) {
-    // The element was removed or has moved to another document since the
-    // |requestFullscreen()| call. Exit fullscreen again to recover.
-    // TODO(foolip): Fire a fullscreenerror event. This is currently difficult
-    // because the fullscreenchange event has already been enqueued and possibly
-    // even fired. https://crbug.com/402376
-    LocalFrame& frame = *GetDocument()->GetFrame();
-    frame.GetChromeClient().ExitFullscreen(frame);
+// https://fullscreen.spec.whatwg.org/#exit-fullscreen
+void Fullscreen::ExitFullscreen(Document& doc, ExitType exit_type) {
+  if (!doc.IsActive() || !doc.GetFrame())
     return;
-  }
 
-  if (full_screen_layout_object_)
-    full_screen_layout_object_->UnwrapLayoutObject();
+  // 1. Let |promise| be a new promise.
+  // 2. If |doc|'s fullscreen element is null, reject |promise| with a
+  // TypeError exception, and return |promise|.
+  // TODO(foolip): Promises. https://crbug.com/644637
+  if (!FullscreenElementFrom(doc))
+    return;
 
-  Element* previous_element = current_full_screen_element_;
-  current_full_screen_element_ = element;
-
-  // Create a placeholder block for a the full-screen element, to keep the page
-  // from reflowing when the element is removed from the normal flow. Only do
-  // this for a LayoutBox, as only a box will have a frameRect. The placeholder
-  // will be created in setFullScreenLayoutObject() during layout.
-  LayoutObject* layout_object = current_full_screen_element_->GetLayoutObject();
-  bool should_create_placeholder = layout_object && layout_object->IsBox();
-  if (should_create_placeholder) {
-    saved_placeholder_frame_rect_ = ToLayoutBox(layout_object)->FrameRect();
-    saved_placeholder_computed_style_ =
-        ComputedStyle::Clone(layout_object->StyleRef());
-  }
+  // 3. Let |resize| be false.
+  bool resize = false;
 
-  // TODO(alexmos): When |m_forCrossProcessDescendant| is true, some of
-  // this layout work has already been done in another process, so it should
-  // not be necessary to repeat it here.
-  if (current_full_screen_element_ != GetDocument()->documentElement()) {
-    LayoutFullScreen::WrapLayoutObject(
-        layout_object, layout_object ? layout_object->Parent() : 0,
-        GetDocument());
-  }
+  // 4. Let |docs| be the result of collecting documents to unfullscreen given
+  // |doc|.
+  HeapVector<Member<Document>> docs =
+      CollectDocumentsToUnfullscreen(doc, exit_type);
 
-  // When |m_forCrossProcessDescendant| is true, m_currentFullScreenElement
-  // corresponds to the HTMLFrameOwnerElement for the out-of-process iframe
-  // that contains the actual fullscreen element.   Hence, it must also set
-  // the ContainsFullScreenElement flag (so that it gains the
-  // -webkit-full-screen-ancestor style).
-  if (for_cross_process_descendant_) {
-    DCHECK(current_full_screen_element_->IsFrameOwnerElement());
-    DCHECK(ToHTMLFrameOwnerElement(current_full_screen_element_)
-               ->ContentFrame()
-               ->IsRemoteFrame());
-    current_full_screen_element_->SetContainsFullScreenElement(true);
+  // 5. Let |topLevelDoc| be |doc|'s top-level browsing context's document.
+  //
+  // OOPIF: Let |topLevelDoc| be the topmost local ancestor instead. If the main
+  // frame is in another process, we will still fully exit fullscreen even
+  // though that's wrong if the main frame was in nested fullscreen.
+  // TODO(alexmos): Deal with nested fullscreen cases, see
+  // https://crbug.com/617369.
+  Document& top_level_doc = TopmostLocalAncestor(doc);
+
+  // 6. If |topLevelDoc| is in |docs|, set |resize| to true.
+  if (!docs.IsEmpty() && docs.back() == &top_level_doc)
+    resize = true;
+
+  // 7. Return |promise|, and run the remaining steps in parallel.
+  // TODO(foolip): Promises. https://crbug.com/644637
+
+  // Note: |ExitType::Fully| is only used together with the topmost local
+  // ancestor in |fullyExitFullscreen()|, and so implies that |resize| is true.
+  // This would change if matching the spec for "fully exit fullscreen".
+  if (exit_type == ExitType::kFully)
+    DCHECK(resize);
+
+  // 8. If |resize| is true, resize |topLevelDoc|'s viewport to its "normal"
+  // dimensions.
+  if (resize) {
+    LocalFrame& frame = *doc.GetFrame();
+    frame.GetChromeClient().ExitFullscreen(frame);
+  } else {
+    EnqueueTaskForExit(doc, exit_type);
   }
+}
 
-  current_full_screen_element_
-      ->SetContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(true);
+void Fullscreen::DidExitFullscreen() {
+  if (!GetDocument())
+    return;
 
-  GetDocument()->GetStyleEngine().EnsureUAStyleForFullscreen();
-  current_full_screen_element_->PseudoStateChanged(
-      CSSSelector::kPseudoFullScreen);
+  DCHECK_EQ(GetDocument(), &TopmostLocalAncestor(*GetDocument()));
 
-  // FIXME: This should not call updateStyleAndLayoutTree.
-  GetDocument()->UpdateStyleAndLayoutTree();
+  EnqueueTaskForExit(*GetDocument(), ExitType::kFully);
+}
 
-  GetDocument()->GetFrame()->GetChromeClient().FullscreenElementChanged(
-      previous_element, element);
+void Fullscreen::EnqueueTaskForExit(Document& document, ExitType exit_type) {
+  // 9. As part of the next animation frame task, run these substeps:
+  document.EnqueueAnimationFrameTask(
+      WTF::Bind(&RunTaskForExit, WrapPersistent(&document), exit_type));
 }
 
-void Fullscreen::DidExitFullscreen() {
-  if (!GetDocument()->IsActive() || !GetDocument()->GetFrame())
+void Fullscreen::RunTaskForExit(Document* document, ExitType exit_type) {
+  DCHECK(document);
+  DCHECK(document->IsActive());
+  DCHECK(document->GetFrame());
+
+  Document& doc = *document;
+
+  if (!FullscreenElementFrom(doc))
     return;
 
-  // Start the timer for events enqueued by |exitFullscreen()|. The hover state
-  // update is scheduled first so that it's done when the events fire.
-  GetDocument()->GetFrame()->GetEventHandler().ScheduleHoverStateUpdate();
-  event_queue_timer_.StartOneShot(0, BLINK_FROM_HERE);
+  // 9.1. Let |exitDocs| be the result of collecting documents to unfullscreen
+  // given |doc|.
 
-  // If fullscreen was canceled by the browser, e.g. if the user pressed Esc,
-  // then |exitFullscreen()| was never called. Let |fullyExitFullscreen()| clear
-  // the fullscreen element stack and fire any events as necessary.
-  // TODO(foolip): Remove this when state changes and events are synchronized
-  // with animation frames. https://crbug.com/402376
-  FullyExitFullscreen(*GetDocument());
+  // 9.2. If |resize| is true and |topLevelDoc| is not in |exitDocs|, fully
+  // exit fullscreen |topLevelDoc|, reject promise with a TypeError exception,
+  // and terminate these steps.
 
-  if (!current_full_screen_element_)
-    return;
+  // TODO(foolip): See TODO in |fullyExitFullscreen()|. Instead of using "fully
+  // exit fullscreen" in step 9.2 (which is async), give "exit fullscreen" a
+  // |fully| flag which is always true if |resize| was true.
 
-  if (for_cross_process_descendant_)
-    current_full_screen_element_->SetContainsFullScreenElement(false);
+  HeapVector<Member<Document>> exit_docs =
+      CollectDocumentsToUnfullscreen(doc, exit_type);
 
-  current_full_screen_element_
-      ->SetContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(false);
+  // 9.3. If |exitDocs| is the empty set, append |doc| to |exitDocs|.
+  if (exit_docs.IsEmpty())
+    exit_docs.push_back(&doc);
 
-  if (full_screen_layout_object_)
-    LayoutFullScreenItem(full_screen_layout_object_).UnwrapLayoutObject();
+  // 9.4. If |exitDocs|'s last document has a browsing context container,
+  // append that browsing context container's node document to |exitDocs|.
+  //
+  // OOPIF: Skip over remote frames, assuming that they have exactly one element
+  // in their fullscreen element stacks, thereby erring on the side of exiting
+  // fullscreen. TODO(alexmos): Deal with nested fullscreen cases, see
+  // https://crbug.com/617369.
+  if (Document* document = NextLocalAncestor(*exit_docs.back()))
+    exit_docs.push_back(document);
+
+  // 9.5. Let |descendantDocs| be an ordered set consisting of |doc|'s
+  // descendant browsing contexts' documents whose fullscreen element is
+  // non-null, if any, in *reverse* tree order.
+  HeapDeque<Member<Document>> descendant_docs;
+  for (Frame* descendant = doc.GetFrame()->Tree().FirstChild(); descendant;
+       descendant = descendant->Tree().TraverseNext(doc.GetFrame())) {
+    if (!descendant->IsLocalFrame())
+      continue;
+    DCHECK(ToLocalFrame(descendant)->GetDocument());
+    if (FullscreenElementFrom(*ToLocalFrame(descendant)->GetDocument()))
+      descendant_docs.push_front(ToLocalFrame(descendant)->GetDocument());
+  }
 
-  GetDocument()->GetStyleEngine().EnsureUAStyleForFullscreen();
-  current_full_screen_element_->PseudoStateChanged(
-      CSSSelector::kPseudoFullScreen);
-  Element* previous_element = current_full_screen_element_;
-  current_full_screen_element_ = nullptr;
+  // Note: For prefixed requests, the event target is an element, so let
+  // |events| be a list of events to dispatch.
+  HeapVector<Member<Event>> events;
+
+  // 9.6. For each |descendantDoc| in |descendantDocs|, in order, unfullscreen
+  // |descendantDoc|.
+  for (Document* descendant_doc : descendant_docs) {
+    Fullscreen& fullscreen = From(*descendant_doc);
+    ElementStack& stack = fullscreen.fullscreen_element_stack_;
+    DCHECK(!stack.IsEmpty());
+    events.push_back(CreateChangeEvent(*descendant_doc, *stack.back().first,
+                                       stack.back().second));
+    while (!stack.IsEmpty())
+      fullscreen.PopFullscreenElementStack();
+  }
 
-  for_cross_process_descendant_ = false;
+  // 9.7. For each |exitDoc| in |exitDocs|, in order, unfullscreen |exitDoc|'s
+  // fullscreen element.
+  for (Document* exit_doc : exit_docs) {
+    Fullscreen& fullscreen = From(*exit_doc);
+    ElementStack& stack = fullscreen.fullscreen_element_stack_;
+    DCHECK(!stack.IsEmpty());
+    events.push_back(
+        CreateChangeEvent(*exit_doc, *stack.back().first, stack.back().second));
+    fullscreen.PopFullscreenElementStack();
+
+    // TODO(foolip): See TODO in |fullyExitFullscreen()|.
+    if (exit_doc == &doc && exit_type == ExitType::kFully) {
+      while (!stack.IsEmpty())
+        fullscreen.PopFullscreenElementStack();
+    }
+  }
 
-  GetDocument()->GetFrame()->GetChromeClient().FullscreenElementChanged(
-      previous_element, nullptr);
+  // 9.8. For each |descendantDoc| in |descendantDocs|, in order, fire an
+  // event named fullscreenchange on |descendantDoc|.
+  // 9.9. For each |exitDoc| in |exitDocs|, in order, fire an event named
+  // fullscreenchange on |exitDoc|.
+  DispatchEvents(events);
+
+  // 9.10. Fulfill |promise| with undefined.
+  // TODO(foolip): Promises. https://crbug.com/644637
+}
+
+// https://fullscreen.spec.whatwg.org/#dom-document-fullscreenenabled
+bool Fullscreen::FullscreenEnabled(Document& document) {
+  // The fullscreenEnabled attribute's getter must return true if the context
+  // object is allowed to use the feature indicated by attribute name
+  // allowfullscreen and fullscreen is supported, and false otherwise.
+  return AllowedToUseFullscreen(document.GetFrame()) &&
+         FullscreenIsSupported(document);
 }
 
 void Fullscreen::SetFullScreenLayoutObject(LayoutFullScreen* layout_object) {
@@ -774,56 +802,9 @@ void Fullscreen::FullScreenLayoutObjectDestroyed() {
   full_screen_layout_object_ = nullptr;
 }
 
-void Fullscreen::EnqueueChangeEvent(Document& document,
-                                    RequestType request_type) {
-  Event* event;
-  if (request_type == RequestType::kUnprefixed) {
-    event = CreateEvent(EventTypeNames::fullscreenchange, document);
-  } else {
-    DCHECK(document.HasFullscreenSupplement());
-    Fullscreen& fullscreen = From(document);
-    EventTarget* target = fullscreen.FullscreenElement();
-    if (!target)
-      target = fullscreen.CurrentFullScreenElement();
-    if (!target)
-      target = &document;
-    event = CreateEvent(EventTypeNames::webkitfullscreenchange, *target);
-  }
-  event_queue_.push_back(event);
-  // NOTE: The timer is started in didEnterFullscreen/didExitFullscreen.
-}
-
-void Fullscreen::EnqueueErrorEvent(Element& element, RequestType request_type) {
-  Event* event;
-  if (request_type == RequestType::kUnprefixed)
-    event = CreateEvent(EventTypeNames::fullscreenerror, element.GetDocument());
-  else
-    event = CreateEvent(EventTypeNames::webkitfullscreenerror, element);
-  event_queue_.push_back(event);
-  event_queue_timer_.StartOneShot(0, BLINK_FROM_HERE);
-}
-
-void Fullscreen::EventQueueTimerFired(TimerBase*) {
-  HeapDeque<Member<Event>> event_queue;
-  event_queue_.Swap(event_queue);
-
-  while (!event_queue.IsEmpty()) {
-    Event* event = event_queue.TakeFirst();
-    Node* target = event->target()->ToNode();
-
-    // If the element was removed from our tree, also message the
-    // documentElement.
-    if (!target->isConnected() && GetDocument()->documentElement()) {
-      DCHECK(IsPrefixed(event->type()));
-      event_queue.push_back(
-          CreateEvent(event->type(), *GetDocument()->documentElement()));
-    }
-
-    target->DispatchEvent(event);
-  }
-}
-
 void Fullscreen::ElementRemoved(Element& node) {
+  DCHECK_EQ(GetDocument(), &node.GetDocument());
+
   // |Fullscreen::ElementRemoved| is called for each removed element, so only
   // the body of the spec "removing steps" loop appears here:
 
@@ -845,36 +826,107 @@ void Fullscreen::ElementRemoved(Element& node) {
   // Note: |node| was not in the fullscreen element stack.
 }
 
-void Fullscreen::ClearFullscreenElementStack() {
-  if (fullscreen_element_stack_.IsEmpty())
-    return;
-
-  fullscreen_element_stack_.clear();
-
-  SetNeedsPaintPropertyUpdate(GetDocument());
-}
-
 void Fullscreen::PopFullscreenElementStack() {
-  if (fullscreen_element_stack_.IsEmpty())
-    return;
+  DCHECK(!fullscreen_element_stack_.IsEmpty());
 
+  Element* previous_element = FullscreenElement();
   fullscreen_element_stack_.pop_back();
 
-  SetNeedsPaintPropertyUpdate(GetDocument());
+  // Note: |requestType| is only used if |fullscreenElement()| is non-null.
+  RequestType request_type = fullscreen_element_stack_.IsEmpty()
+                                 ? RequestType::kUnprefixed
+                                 : fullscreen_element_stack_.back().second;
+  FullscreenElementChanged(previous_element, FullscreenElement(), request_type);
 }
 
 void Fullscreen::PushFullscreenElementStack(Element& element,
                                             RequestType request_type) {
+  Element* previous_element = FullscreenElement();
   fullscreen_element_stack_.push_back(std::make_pair(&element, request_type));
 
-  SetNeedsPaintPropertyUpdate(GetDocument());
+  FullscreenElementChanged(previous_element, &element, request_type);
+}
+
+void Fullscreen::FullscreenElementChanged(Element* from_element,
+                                          Element* to_element,
+                                          RequestType to_request_type) {
+  DCHECK_NE(from_element, to_element);
+
+  if (!GetDocument())
+    return;
+
+  GetDocument()->GetStyleEngine().EnsureUAStyleForFullscreen();
+
+  if (full_screen_layout_object_)
+    full_screen_layout_object_->UnwrapLayoutObject();
+  DCHECK(!full_screen_layout_object_);
+
+  if (from_element) {
+    DCHECK_NE(from_element, FullscreenElement());
+
+    from_element->PseudoStateChanged(CSSSelector::kPseudoFullScreen);
+
+    from_element->SetContainsFullScreenElement(false);
+    from_element
+        ->SetContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(false);
+  }
+
+  if (to_element) {
+    DCHECK_EQ(to_element, FullscreenElement());
+
+    to_element->PseudoStateChanged(CSSSelector::kPseudoFullScreen);
+
+    // OOPIF: For RequestType::PrefixedForCrossProcessDescendant, |toElement| is
+    // the iframe element for the out-of-process frame that contains the
+    // fullscreen element. Hence, it must match :-webkit-full-screen-ancestor.
+    if (to_request_type == RequestType::kPrefixedForCrossProcessDescendant) {
+      DCHECK(isHTMLIFrameElement(to_element));
+      to_element->SetContainsFullScreenElement(true);
+    }
+    to_element->SetContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(
+        true);
+
+    // Create a placeholder block for the fullscreen element, to keep the page
+    // from reflowing when the element is removed from the normal flow. Only do
+    // this for a LayoutBox, as only a box will have a frameRect. The
+    // placeholder will be created in setFullScreenLayoutObject() during layout.
+    LayoutObject* layout_object = to_element->GetLayoutObject();
+    bool should_create_placeholder = layout_object && layout_object->IsBox();
+    if (should_create_placeholder) {
+      saved_placeholder_frame_rect_ = ToLayoutBox(layout_object)->FrameRect();
+      saved_placeholder_computed_style_ =
+          ComputedStyle::Clone(layout_object->StyleRef());
+    }
+
+    if (to_element != GetDocument()->documentElement()) {
+      LayoutFullScreen::WrapLayoutObject(
+          layout_object, layout_object ? layout_object->Parent() : 0,
+          GetDocument());
+    }
+  }
+
+  if (LocalFrame* frame = GetDocument()->GetFrame()) {
+    // TODO(foolip): Synchronize hover state changes with animation frames.
+    // https://crbug.com/668758
+    frame->GetEventHandler().ScheduleHoverStateUpdate();
+    frame->GetChromeClient().FullscreenElementChanged(from_element, to_element);
+
+    if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled() &&
+        !RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
+      // Fullscreen status affects scroll paint properties through
+      // LocalFrameView::UserInputScrollable().
+      if (LocalFrameView* frame_view = frame->View())
+        frame_view->SetNeedsPaintPropertyUpdate();
+    }
+  }
+
+  // TODO(foolip): This should not call updateStyleAndLayoutTree.
+  GetDocument()->UpdateStyleAndLayoutTree();
 }
 
 DEFINE_TRACE(Fullscreen) {
-  visitor->Trace(pending_fullscreen_element_);
+  visitor->Trace(pending_requests_);
   visitor->Trace(fullscreen_element_stack_);
-  visitor->Trace(current_full_screen_element_);
-  visitor->Trace(event_queue_);
   Supplement<Document>::Trace(visitor);
   ContextLifecycleObserver::Trace(visitor);
 }