[Media controls] Add rotate-to-fullscreen gesture behind flag

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/ElementVisibilityObserver.h"
 
 #include "core/dom/Element.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "core/frame/LocalFrame.h"
 #include "platform/wtf/Functional.h"
 
 namespace blink {
 
 ElementVisibilityObserver::ElementVisibilityObserver(
     Element* element,
     std::unique_ptr<VisibilityCallback> callback)
     : element_(element), callback_(std::move(callback)) {}
 
 ElementVisibilityObserver::~ElementVisibilityObserver() = default;
 
-void ElementVisibilityObserver::Start() {
+void ElementVisibilityObserver::Start(float threshold) {
   DCHECK(!intersection_observer_);
 
   ExecutionContext* context = element_->GetExecutionContext();
   DCHECK(context->IsDocument());
   Document& document = ToDocument(*context);
 
   intersection_observer_ = IntersectionObserver::Create(
-      Vector<Length>(), Vector<float>({std::numeric_limits<float>::min()}),
-      &document,
+      {} /* root_margin */, {threshold}, &document,
       WTF::Bind(&ElementVisibilityObserver::OnVisibilityChanged,
                 WrapWeakPersistent(this)));
   DCHECK(intersection_observer_);
 
   intersection_observer_->observe(element_.Release());
 }
 
 void ElementVisibilityObserver::Stop() {
   DCHECK(intersection_observer_);
 
   intersection_observer_->disconnect();
   intersection_observer_ = nullptr;
 }
 
 void ElementVisibilityObserver::DeliverObservationsForTesting() {
   intersection_observer_->Deliver();
 }
 
 DEFINE_TRACE(ElementVisibilityObserver) {
   visitor->Trace(element_);
   visitor->Trace(intersection_observer_);
 }
 
 void ElementVisibilityObserver::OnVisibilityChanged(
     const HeapVector<Member<IntersectionObserverEntry>>& entries) {
-  bool is_visible = entries.back()->intersectionRatio() > 0.f;
+  bool is_visible = entries.back()->intersectionRatio() >
+                    intersection_observer_->thresholds()[0];
   (*callback_.get())(is_visible);
 }
 
 }  // namespace blink