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 60a91662e467be9ae73c67779cbf7953b6b55943..5cdae3e3d8347e5ee3e68901e6d3b87a94aebad3 100644
--- a/third_party/WebKit/Source/core/dom/Fullscreen.cpp
+++ b/third_party/WebKit/Source/core/dom/Fullscreen.cpp
@@ -181,19 +181,6 @@ bool fullscreenElementReady(const Element& element) {
   return true;
 }
 
-bool isPrefixed(const AtomicString& type) {
-  return type == EventTypeNames::webkitfullscreenchange ||
-         type == EventTypeNames::webkitfullscreenerror;
-}
-
-Event* createEvent(const AtomicString& type, EventTarget& target) {
-  EventInit initializer;
-  initializer.setBubbles(isPrefixed(type));
-  Event* event = Event::create(type, initializer);
-  event->setTarget(&target);
-  return event;
-}
-
 // Walks the frame tree and returns the first local ancestor frame, if any.
 LocalFrame* nextLocalAncestor(Frame& frame) {
   Frame* parent = frame.tree().parent();
@@ -228,16 +215,99 @@ 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.frame();
-  while (frame->tree().parent() != doc.frame())
-    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 exitType) {
+  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 (exitType != Fullscreen::ExitType::Fully &&
+      Fullscreen::fullscreenElementStackSizeFrom(doc) > 1)
+    return HeapVector<Member<Document>>();
+
+  // 2. Let |docs| be an ordered set consisting of |doc|.
+  HeapVector<Member<Document>> docs;
+  docs.append(&doc);
+
+  // 3. While |docs|'s last 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
+
+  // 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)) {
+    if (Fullscreen::fullscreenElementStackSizeFrom(*document) == 1)
+      docs.append(document);
+    else
+      break;
+  }
+
+  // 4. Return |docs|.
+  return docs;
+}
+
+// Creates a non-bubbling event with |document| as its target.
+Event* createEvent(const AtomicString& type, Document& document) {
+  DCHECK(type == EventTypeNames::fullscreenchange ||
+         type == EventTypeNames::fullscreenerror);
+
+  Event* event = Event::create(type);
+  event->setTarget(&document);
+  return event;
+}
+
+// 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.document() == document)
+    event->setTarget(&element);
+  else
+    event->setTarget(&document);
+  return event;
+}
+
+Event* createChangeEvent(Document& document,
+                         Element& element,
+                         Fullscreen::RequestType requestType) {
+  if (requestType == Fullscreen::RequestType::Unprefixed)
+    return createEvent(EventTypeNames::fullscreenchange, document);
+  return createPrefixedEvent(EventTypeNames::webkitfullscreenchange, element,
+                             document);
+}
+
+Event* createErrorEvent(Document& document,
+                        Element& element,
+                        Fullscreen::RequestType requestType) {
+  if (requestType == Fullscreen::RequestType::Unprefixed)
+    return createEvent(EventTypeNames::fullscreenerror, document);
+  return createPrefixedEvent(EventTypeNames::webkitfullscreenerror, element,
+                             document);
+}
+
+void dispatchEvent(Event* event) {
+  event->target()->dispatchEvent(event);
+}
+
+void dispatchEvents(const HeapVector<Member<Event>>& events) {
+  for (Event* event : events)
+    dispatchEvent(event);
 }
 
 }  // anonymous namespace
@@ -267,6 +337,12 @@ Element* Fullscreen::fullscreenElementFrom(Document& document) {
   return nullptr;
 }
 
+size_t Fullscreen::fullscreenElementStackSizeFrom(Document& document) {
+  if (Fullscreen* found = fromIfExists(document))
+    return found->m_fullscreenElementStack.size();
+  return 0;
+}
+
 Element* Fullscreen::fullscreenElementForBindingFrom(TreeScope& scope) {
   Element* element = fullscreenElementFrom(scope.document());
   if (!element || !RuntimeEnabledFeatures::fullscreenUnprefixedEnabled())
@@ -288,63 +364,41 @@ 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::DocumentFullscreenElementInV0Shadow);
-    return element;
-  }
-  return document.adjustedElement(*element);
-}
-
 Fullscreen::Fullscreen(Document& document)
-    : ContextLifecycleObserver(&document),
-      m_fullScreenLayoutObject(nullptr),
-      m_eventQueueTimer(this, &Fullscreen::eventQueueTimerFired),
-      m_forCrossProcessDescendant(false) {
+    : ContextLifecycleObserver(&document), m_fullScreenLayoutObject(nullptr) {
   document.setHasFullscreenSupplement();
 }
 
 Fullscreen::~Fullscreen() {}
 
-inline Document* Fullscreen::document() {
+Document* Fullscreen::document() {
   return toDocument(lifecycleContext());
 }
 
 void Fullscreen::contextDestroyed() {
-  m_eventQueue.clear();
-
   if (m_fullScreenLayoutObject)
     m_fullScreenLayoutObject->destroy();
 
-  m_currentFullScreenElement = nullptr;
+  m_pendingRequests.clear();
   m_fullscreenElementStack.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::Prefixed, false);
+  requestFullscreen(pending, RequestType::Prefixed);
 }
 
-void Fullscreen::requestFullscreen(Element& element,
-                                   RequestType requestType,
-                                   bool forCrossProcessDescendant) {
-  Document& document = element.document();
+void Fullscreen::requestFullscreen(Element& pending, RequestType requestType) {
+  Document& document = pending.document();
+
+  // Ignore this call if the document is not in a live frame.
+  if (!document.isActive() || !document.frame())
+    return;
+
+  bool forCrossProcessDescendant =
+      requestType == RequestType::PrefixedForCrossProcessDescendant;
 
   // Use counters only need to be incremented in the process of the actual
   // fullscreen element.
@@ -358,28 +412,31 @@ void Fullscreen::requestFullscreen(Element& element,
     }
   }
 
-  // Ignore this call if the document is not in a live frame.
-  if (!document.isActive() || !document.frame())
-    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;
+
+  // 3. Let |promise| be a new promise.
+  // TODO(foolip): Promises. https://crbug.com/644637
 
   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:
-
-    // |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))
+    // OOPIF: If |requestFullscreen()| was already called in descendant frame
+    // and passed the checks, do not check again here.
+    if (forCrossProcessDescendant)
+      break;
+
+    // 4. If any of the following conditions are false, then set |error| to
+    // true:
+    error = true;
+
+    // |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))
       break;
 
-    // The fullscreen element ready check for |element| returns true.
-    if (!fullscreenElementReady(element))
+    // The fullscreen element ready check for |pending| returns false.
+    if (!fullscreenElementReady(pending))
       break;
 
     // Fullscreen is supported.
@@ -387,326 +444,306 @@ void Fullscreen::requestFullscreen(Element& element,
       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 (!forCrossProcessDescendant && !allowedToRequestFullscreen(document))
+    if (!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.prepend(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* currentDoc = *current;
-      Document* followingDoc = 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 (!followingDoc) {
-        from(*currentDoc).pushFullscreenElementStack(element, requestType);
-        from(document).enqueueChangeEvent(*currentDoc, requestType);
-        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* topElement = fullscreenElementFrom(*currentDoc);
-      HTMLFrameOwnerElement* followingOwner =
-          findContainerForDescendant(*currentDoc, *followingDoc);
-      if (!topElement || topElement != followingOwner) {
-        // ...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(*currentDoc)
-            .pushFullscreenElementStack(*followingOwner, requestType);
-        from(document).enqueueChangeEvent(*currentDoc, requestType);
-        continue;
-      }
-
-      // 4. Otherwise, do nothing for this document. It stays the same.
-    } while (++current != docs.end());
-
-    from(document).m_forCrossProcessDescendant = forCrossProcessDescendant;
-
-    // 5. Return, and run the remaining steps asynchronously.
-    // 6. Optionally, perform some animation.
-    from(document).m_pendingFullscreenElement = &element;
-    document.frame()->chromeClient().enterFullscreen(*document.frame());
-
-    // 7. Optionally, display a message indicating how the user can exit
-    // displaying the context object fullscreen.
-    return;
+    error = false;
   } while (false);
 
-  from(document).enqueueErrorEvent(element, requestType);
+  // 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) {
+    from(document).m_pendingRequests.append(
+        std::make_pair(&pending, requestType));
+    LocalFrame& frame = *document.frame();
+    frame.chromeClient().enterFullscreen(frame);
+  } else {
+    enqueueTaskForRequest(document, pending, requestType, 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))
-    return;
-
-  // 3. Remove elements from |doc|'s fullscreen element stack until only the top
-  // element is left.
-  size_t stackSize = from(doc).m_fullscreenElementStack.size();
-  from(doc).m_fullscreenElementStack.remove(0, stackSize - 1);
-  DCHECK_EQ(from(doc).m_fullscreenElementStack.size(), 1u);
-
-  // 4. Act as if the exitFullscreen() method was invoked on |doc|.
-  exitFullscreen(doc);
+void Fullscreen::didEnterFullscreen() {
+  ElementStack requests;
+  requests.swap(m_pendingRequests);
+  for (const ElementStackEntry& request : requests)
+    enqueueTaskForRequest(*document(), *request.first, request.second, false);
 }
 
-// https://fullscreen.spec.whatwg.org/#exit-fullscreen
-void Fullscreen::exitFullscreen(Document& document) {
-  // The exitFullscreen() method must run these steps:
-
-  // Ignore this call if the document is not in a live frame.
-  if (!document.isActive() || !document.frame())
-    return;
+void Fullscreen::enqueueTaskForRequest(Document& document,
+                                       Element& pending,
+                                       RequestType requestType,
+                                       bool error) {
+  // 7. As part of the next animation frame task, run these substeps:
+  document.enqueueAnimationFrameTask(
+      WTF::bind(&runTaskForRequest, wrapPersistent(&document),
+                wrapPersistent(&pending), requestType, error));
+}
 
-  // 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))
+void Fullscreen::runTaskForRequest(Document* document,
+                                   Element* element,
+                                   RequestType requestType,
+                                   bool error) {
+  DCHECK(document);
+  DCHECK(element);
+  Document& pendingDoc = *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.document() != pendingDoc)
+    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)) {
+    dispatchEvent(createErrorEvent(pendingDoc, pending, requestType));
     return;
-
-  // 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.frame()->tree().traverseNext(); descendant;
-       descendant = descendant->tree().traverseNext()) {
-    if (!descendant->isLocalFrame())
-      continue;
-    DCHECK(toLocalFrame(descendant)->document());
-    if (fullscreenElementFrom(*toLocalFrame(descendant)->document()))
-      descendants.prepend(toLocalFrame(descendant)->document());
   }
 
-  // 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 requestType =
-        from(*descendant).m_fullscreenElementStack.back().second;
-    from(*descendant).clearFullscreenElementStack();
-    from(document).enqueueChangeEvent(*descendant, requestType);
-  }
+  // 7.2. Let |fullscreenElements| be an ordered set initially consisting of
+  // |pending|.
+  HeapDeque<Member<Element>> fullscreenElements;
+  fullscreenElements.append(pending);
 
-  // 5. While doc is not null, run these substeps:
-  Element* newTop = nullptr;
-  for (Document* currentDoc = &document; currentDoc;) {
-    RequestType requestType =
-        from(*currentDoc).m_fullscreenElementStack.back().second;
+  // 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.document().frame(); frame;
+       frame = frame->tree().parent()) {
+    if (frame->owner() && frame->owner()->isLocal()) {
+      Element* element = toHTMLFrameOwnerElement(frame->owner());
+      fullscreenElements.prepend(element);
+    }
+  }
 
-    // 1. Pop the top element of doc's fullscreen element stack.
-    from(*currentDoc).popFullscreenElementStack();
+  // 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;
 
-    //    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.
-    newTop = fullscreenElementFrom(*currentDoc);
-    if (newTop && (!newTop->isConnected() || newTop->document() != currentDoc))
-      continue;
+  // 7.5. For each |element| in |fullscreenElements|, in order, run these
+  // subsubsteps:
+  for (Element* element : fullscreenElements) {
+    // 7.5.1. Let |doc| be |element|'s node document.
+    Document& doc = element->document();
 
-    // 2. Queue a task to fire an event named fullscreenchange with its bubbles
-    // attribute set to true on doc.
-    from(document).enqueueChangeEvent(*currentDoc, requestType);
-
-    // 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 (!newTop) {
-      currentDoc = nextLocalAncestor(*currentDoc);
+    // 7.5.2. If |element| is |doc|'s fullscreen element, terminate these
+    // subsubsteps.
+    if (element == fullscreenElementFrom(doc))
       continue;
-    }
 
-    // 4. Otherwise, set doc to null.
-    currentDoc = nullptr;
-  }
+    // 7.5.3. Otherwise, append |doc| to |eventDocs|.
+    events.append(createChangeEvent(doc, *element, requestType));
 
-  // 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 (!newTop) {
-    document.frame()->chromeClient().exitFullscreen(*document.frame());
-    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, requestType);
   }
 
-  // Otherwise, enter fullscreen for the fullscreen element stack's top element.
-  from(document).m_pendingFullscreenElement = newTop;
-  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.frame()) &&
-         fullscreenIsSupported(document);
+  // 7.7. Fulfill |promise| with undefined.
+  // TODO(foolip): Promises. https://crbug.com/644637
 }
 
-void Fullscreen::didEnterFullscreen() {
-  if (!document()->isActive() || !document()->frame())
-    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.
-  document()->frame()->eventHandler().scheduleHoverStateUpdate();
-  m_eventQueueTimer.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 = m_pendingFullscreenElement.release();
-  if (!element)
-    return;
+  // 3. Exit fullscreen |document|.
 
-  if (m_currentFullScreenElement == 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::Fully);
+}
 
-  if (!element->isConnected() || &element->document() != document()) {
-    // 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 = *document()->frame();
-    frame.chromeClient().exitFullscreen(frame);
+// https://fullscreen.spec.whatwg.org/#exit-fullscreen
+void Fullscreen::exitFullscreen(Document& doc, ExitType exitType) {
+  if (!doc.isActive() || !doc.frame())
     return;
-  }
 
-  if (m_fullScreenLayoutObject)
-    m_fullScreenLayoutObject->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* previousElement = m_currentFullScreenElement;
-  m_currentFullScreenElement = 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* layoutObject = m_currentFullScreenElement->layoutObject();
-  bool shouldCreatePlaceholder = layoutObject && layoutObject->isBox();
-  if (shouldCreatePlaceholder) {
-    m_savedPlaceholderFrameRect = toLayoutBox(layoutObject)->frameRect();
-    m_savedPlaceholderComputedStyle =
-        ComputedStyle::clone(layoutObject->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 (m_currentFullScreenElement != document()->documentElement())
-    LayoutFullScreen::wrapLayoutObject(
-        layoutObject, layoutObject ? layoutObject->parent() : 0, document());
-
-  // 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 (m_forCrossProcessDescendant) {
-    DCHECK(m_currentFullScreenElement->isFrameOwnerElement());
-    DCHECK(toHTMLFrameOwnerElement(m_currentFullScreenElement)
-               ->contentFrame()
-               ->isRemoteFrame());
-    m_currentFullScreenElement->setContainsFullScreenElement(true);
-  }
+  // 4. Let |docs| be the result of collecting documents to unfullscreen given
+  // |doc|.
+  HeapVector<Member<Document>> docs =
+      collectDocumentsToUnfullscreen(doc, exitType);
 
-  m_currentFullScreenElement
-      ->setContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(true);
+  // 5. Let |topLevelDoc| be |doc|'s top-level browsing context's document.
 
-  document()->styleEngine().ensureUAStyleForFullscreen();
-  m_currentFullScreenElement->pseudoStateChanged(CSSSelector::PseudoFullScreen);
+  // 6. If |topLevelDoc| is in |docs|, set |resize| to true.
+  // OOPIF: Use |isLocalRoot| as oppposed to |isMainFrame|, so that 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.
+  if (!docs.isEmpty() && docs.back()->frame()->isLocalRoot())
+    resize = true;
 
-  // FIXME: This should not call updateStyleAndLayoutTree.
-  document()->updateStyleAndLayoutTree();
+  // 7. Return |promise|, and run the remaining steps in parallel.
+  // TODO(foolip): Promises. https://crbug.com/644637
 
-  document()->frame()->chromeClient().fullscreenElementChanged(previousElement,
-                                                               element);
+  // 8. If |resize| is true, resize |topLevelDoc|'s viewport to its "normal"
+  // dimensions.
+  if (resize) {
+    LocalFrame& frame = *doc.frame();
+    frame.chromeClient().exitFullscreen(frame);
+  } else {
+    enqueueTaskForExit(doc, exitType);
+  }
 }
 
 void Fullscreen::didExitFullscreen() {
-  if (!document()->isActive() || !document()->frame())
-    return;
+  DCHECK(document());
+  DCHECK_EQ(document(), &topmostLocalAncestor(*document()));
+
+  enqueueTaskForExit(*document(), ExitType::Fully);
+}
 
-  // Start the timer for events enqueued by |exitFullscreen()|. The hover state
-  // update is scheduled first so that it's done when the events fire.
-  document()->frame()->eventHandler().scheduleHoverStateUpdate();
-  m_eventQueueTimer.startOneShot(0, BLINK_FROM_HERE);
+void Fullscreen::enqueueTaskForExit(Document& document, ExitType exitType) {
+  // 9. As part of the next animation frame task, run these substeps:
+  document.enqueueAnimationFrameTask(
+      WTF::bind(&runTaskForExit, wrapPersistent(&document), exitType));
+}
 
-  // 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(*document());
+void Fullscreen::runTaskForExit(Document* document, ExitType exitType) {
+  DCHECK(document);
+  Document& doc = *document;
 
-  if (!m_currentFullScreenElement)
+  if (!fullscreenElementFrom(doc))
     return;
 
-  if (m_forCrossProcessDescendant)
-    m_currentFullScreenElement->setContainsFullScreenElement(false);
+  // 9.1. Let |exitDocs| be the result of collecting documents to unfullscreen
+  // given |doc|.
+
+  // 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.
+
+  // 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.
+
+  HeapVector<Member<Document>> exitDocs =
+      collectDocumentsToUnfullscreen(doc, exitType);
+
+  // 9.3. If |exitDocs| is the empty set, append |doc| to |exitDocs|.
+  if (exitDocs.isEmpty())
+    exitDocs.append(&doc);
+
+  // 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(*exitDocs.back()))
+    exitDocs.append(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>> descendantDocs;
+  for (Frame* descendant = doc.frame()->tree().firstChild(); descendant;
+       descendant = descendant->tree().traverseNext(doc.frame())) {
+    if (!descendant->isLocalFrame())
+      continue;
+    DCHECK(toLocalFrame(descendant)->document());
+    if (fullscreenElementFrom(*toLocalFrame(descendant)->document()))
+      descendantDocs.prepend(toLocalFrame(descendant)->document());
+  }
 
-  m_currentFullScreenElement
-      ->setContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(false);
+  // 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* descendantDoc : descendantDocs) {
+    Fullscreen& fullscreen = from(*descendantDoc);
+    ElementStack& stack = fullscreen.m_fullscreenElementStack;
+    DCHECK(!stack.isEmpty());
+    events.append(createChangeEvent(*descendantDoc, *stack.back().first,
+                                    stack.back().second));
+    while (!stack.isEmpty())
+      fullscreen.popFullscreenElementStack();
+  }
 
-  if (m_fullScreenLayoutObject)
-    LayoutFullScreenItem(m_fullScreenLayoutObject).unwrapLayoutObject();
+  // 9.7. For each |exitDoc| in |exitDocs|, in order, unfullscreen |exitDoc|'s
+  // fullscreen element.
+  for (Document* exitDoc : exitDocs) {
+    Fullscreen& fullscreen = from(*exitDoc);
+    ElementStack& stack = fullscreen.m_fullscreenElementStack;
+    DCHECK(!stack.isEmpty());
+    events.append(
+        createChangeEvent(*exitDoc, *stack.back().first, stack.back().second));
+    fullscreen.popFullscreenElementStack();
+
+    // TODO(foolip): See TODO in |fullyExitFullscreen()|.
+    if (exitDoc == &doc && exitType == ExitType::Fully) {
+      while (!stack.isEmpty())
+        fullscreen.popFullscreenElementStack();
+    }
+  }
 
-  document()->styleEngine().ensureUAStyleForFullscreen();
-  m_currentFullScreenElement->pseudoStateChanged(CSSSelector::PseudoFullScreen);
-  Element* previousElement = m_currentFullScreenElement;
-  m_currentFullScreenElement = 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);
 
-  m_forCrossProcessDescendant = false;
+  // 9.10. Fulfill |promise| with undefined.
+  // TODO(foolip): Promises. https://crbug.com/644637
+}
 
-  document()->frame()->chromeClient().fullscreenElementChanged(previousElement,
-                                                               nullptr);
+// 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.frame()) &&
+         fullscreenIsSupported(document);
 }
 
 void Fullscreen::setFullScreenLayoutObject(LayoutFullScreen* layoutObject) {
@@ -735,56 +772,9 @@ void Fullscreen::fullScreenLayoutObjectDestroyed() {
   m_fullScreenLayoutObject = nullptr;
 }
 
-void Fullscreen::enqueueChangeEvent(Document& document,
-                                    RequestType requestType) {
-  Event* event;
-  if (requestType == RequestType::Unprefixed) {
-    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);
-  }
-  m_eventQueue.append(event);
-  // NOTE: The timer is started in didEnterFullscreen/didExitFullscreen.
-}
-
-void Fullscreen::enqueueErrorEvent(Element& element, RequestType requestType) {
-  Event* event;
-  if (requestType == RequestType::Unprefixed)
-    event = createEvent(EventTypeNames::fullscreenerror, element.document());
-  else
-    event = createEvent(EventTypeNames::webkitfullscreenerror, element);
-  m_eventQueue.append(event);
-  m_eventQueueTimer.startOneShot(0, BLINK_FROM_HERE);
-}
-
-void Fullscreen::eventQueueTimerFired(TimerBase*) {
-  HeapDeque<Member<Event>> eventQueue;
-  m_eventQueue.swap(eventQueue);
-
-  while (!eventQueue.isEmpty()) {
-    Event* event = eventQueue.takeFirst();
-    Node* target = event->target()->toNode();
-
-    // If the element was removed from our tree, also message the
-    // documentElement.
-    if (!target->isConnected() && document()->documentElement()) {
-      DCHECK(isPrefixed(event->type()));
-      eventQueue.append(
-          createEvent(event->type(), *document()->documentElement()));
-    }
-
-    target->dispatchEvent(event);
-  }
-}
-
 void Fullscreen::elementRemoved(Element& oldNode) {
+  DCHECK(document() == &oldNode.document());
+
   // Whenever the removing steps run with an |oldNode| and |oldNode| is in its
   // node document's fullscreen element stack, run these steps:
 
@@ -807,27 +797,95 @@ void Fullscreen::elementRemoved(Element& oldNode) {
   // NOTE: |oldNode| was not in the fullscreen element stack.
 }
 
-void Fullscreen::clearFullscreenElementStack() {
-  m_fullscreenElementStack.clear();
-}
-
 void Fullscreen::popFullscreenElementStack() {
-  if (m_fullscreenElementStack.isEmpty())
-    return;
+  DCHECK(!m_fullscreenElementStack.isEmpty());
 
+  Element* previousElement = fullscreenElement();
   m_fullscreenElementStack.pop_back();
+
+  // Note: |requestType| is only used if |fullscreenElement()| is non-null.
+  RequestType requestType = m_fullscreenElementStack.isEmpty()
+                                ? RequestType::Unprefixed
+                                : m_fullscreenElementStack.back().second;
+  fullscreenElementChanged(previousElement, fullscreenElement(), requestType);
 }
 
 void Fullscreen::pushFullscreenElementStack(Element& element,
                                             RequestType requestType) {
+  Element* previousElement = fullscreenElement();
   m_fullscreenElementStack.append(std::make_pair(&element, requestType));
+
+  fullscreenElementChanged(previousElement, &element, requestType);
+}
+
+void Fullscreen::fullscreenElementChanged(Element* fromElement,
+                                          Element* toElement,
+                                          RequestType toRequestType) {
+  DCHECK_NE(fromElement, toElement);
+
+  document()->styleEngine().ensureUAStyleForFullscreen();
+
+  if (m_fullScreenLayoutObject)
+    m_fullScreenLayoutObject->unwrapLayoutObject();
+  DCHECK(!m_fullScreenLayoutObject);
+
+  if (fromElement) {
+    DCHECK_NE(fromElement, fullscreenElement());
+
+    fromElement->pseudoStateChanged(CSSSelector::PseudoFullScreen);
+
+    fromElement->setContainsFullScreenElement(false);
+    fromElement->setContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(
+        false);
+  }
+
+  if (toElement) {
+    DCHECK_EQ(toElement, fullscreenElement());
+
+    toElement->pseudoStateChanged(CSSSelector::PseudoFullScreen);
+
+    // 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 (toRequestType == RequestType::PrefixedForCrossProcessDescendant) {
+      DCHECK(isHTMLIFrameElement(toElement));
+      toElement->setContainsFullScreenElement(true);
+    }
+    toElement->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* layoutObject = toElement->layoutObject();
+    bool shouldCreatePlaceholder = layoutObject && layoutObject->isBox();
+    if (shouldCreatePlaceholder) {
+      m_savedPlaceholderFrameRect = toLayoutBox(layoutObject)->frameRect();
+      m_savedPlaceholderComputedStyle =
+          ComputedStyle::clone(layoutObject->styleRef());
+    }
+
+    if (toElement != document()->documentElement()) {
+      LayoutFullScreen::wrapLayoutObject(
+          layoutObject, layoutObject ? layoutObject->parent() : 0, document());
+    }
+  }
+
+  if (LocalFrame* frame = document()->frame()) {
+    // TODO(foolip): Synchronize hover state changes with animation frames.
+    // https://crbug.com/668758
+    frame->eventHandler().scheduleHoverStateUpdate();
+    frame->chromeClient().fullscreenElementChanged(fromElement, toElement);
+  }
+
+  // TODO(foolip): This should not call updateStyleAndLayoutTree.
+  document()->updateStyleAndLayoutTree();
 }
 
 DEFINE_TRACE(Fullscreen) {
-  visitor->trace(m_pendingFullscreenElement);
+  visitor->trace(m_pendingRequests);
   visitor->trace(m_fullscreenElementStack);
-  visitor->trace(m_currentFullScreenElement);
-  visitor->trace(m_eventQueue);
   Supplement<Document>::trace(visitor);
   ContextLifecycleObserver::trace(visitor);
 }