Monitor the intersection of video and viewport.

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

Index: third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
index 32ef04c78978b5f0856a4812c1ff8499585d1e5d..16dabe16eb5fd8deadc5bec097a0959bdea30ee4 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
@@ -204,7 +204,8 @@ IntersectionObserver::IntersectionObserver(
       m_rightMargin(Fixed),
       m_bottomMargin(Fixed),
       m_leftMargin(Fixed),
-      m_initialState(InitialState::kHidden) {
+      m_initialState(InitialState::kHidden),
+      m_observeViewportIntersection(thresholds.isEmpty()) {
   switch (rootMargin.size()) {
     case 0:
       break;
@@ -269,7 +270,9 @@ void IntersectionObserver::observe(Element* target,
   LocalFrame* targetFrame = target->document().frame();
   LocalFrame* rootFrame = m_root->document().frame();
 
-  if (target->document() == rootNode()->document()) {
+  if (m_observeViewportIntersection) {

[szager1, 2016/11/16 21:37:55]

Hmm... you're using m_observerViewportIntersection as a kind of hacky
alternative to sub-classing IntersectionObserver.  I think you should just
sub-class IntersectionObserver.  Something like:

class IntersectionObserver {
...
  protected:
    virtual IntersectionObservation* createObservation(Element& target, bool
shouldReportRootBounds) final {
      return new IntersectionObservation(*this, target, shouldReportRootBounds);
    }
}

class ViewportIntersectionObserver : public IntersectionObserver {
  protected:
    IntersectionObservation* createObservation(Element& target, bool) {
      return new ViewportIntersectionObservation(*this, target);
    }
}

void IntersectionObserver::observe(...) {
  ...
  IntersectionObservation* observation = createObservation(*target,
shouldReportRootBounds);
  ...
}

[xjz, 2016/11/16 22:57:15]

Done.

+    shouldReportRootBounds = true;
+  } else if (target->document() == rootNode()->document()) {
     shouldReportRootBounds = true;
     isDOMDescendant = rootNode()->isShadowIncludingInclusiveAncestorOf(target);
   } else if (targetFrame && rootFrame) {
@@ -279,8 +282,13 @@ void IntersectionObserver::observe(Element* target,
     isDOMDescendant = (targetFrame->tree().top() == rootFrame);
   }
 
-  IntersectionObservation* observation =
-      new IntersectionObservation(*this, *target, shouldReportRootBounds);
+  IntersectionObservation* observation;
+  if (m_observeViewportIntersection) {
+    observation = new ViewportIntersectionObservation(*this, *target);
+  } else {
+    observation =
+        new IntersectionObservation(*this, *target, shouldReportRootBounds);
+  }
   target->ensureIntersectionObserverData().addObservation(*observation);
   m_observations.add(observation);