[Picture in Picture] Fix resize observer crash

Fix resize observer crash in PiP interstitial when
we detach, re-attach and detach the video element.

BUG=870449

Change-Id: I6989587384cf34c5b6da8cbaec3ab8ca48b58f94
Reviewed-on: https://chromium-review.googlesource.com/1162514Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580628}

third_party/blink/renderer/core/html/media/html_video_element_test.cc

@@ -74,4 +74,21 @@ TEST_F(HTMLVideoElementTest, PictureInPictureInterstitialAndTextContainer) {
   SetFakeCcLayer(nullptr);
 }
 
+TEST_F(HTMLVideoElementTest, PictureInPictureInterstitial_Reattach) {
+  scoped_refptr<cc::Layer> layer = cc::Layer::Create();
+  SetFakeCcLayer(layer.get());
+
+  video()->SetBooleanAttribute(HTMLNames::controlsAttr, true);
+  video()->SetSrc("http://example.com/foo.mp4");
+  test::RunPendingTasks();
+
+  // Simulate entering Picture-in-Picture.
+  video()->OnEnteredPictureInPicture();
+
+  // Try detaching and reattaching. This should not crash.
+  GetDocument().body()->removeChild(video());
+  GetDocument().body()->appendChild(video());
+  GetDocument().body()->removeChild(video());
+}
+
 }  // namespace blink

third_party/blink/renderer/core/html/media/picture_in_picture_interstitial.cc

@@ -116,11 +116,25 @@ void PictureInPictureInterstitial::Hide() {
     GetVideoElement().CcLayer()->SetIsDrawable(true);
 }
 
+Node::InsertionNotificationRequest PictureInPictureInterstitial::InsertedInto(
+    ContainerNode* root) {
+  if (GetVideoElement().isConnected() && !resize_observer_) {
+    resize_observer_ =
+        ResizeObserver::Create(GetVideoElement().GetDocument(),
+                               new VideoElementResizeObserverDelegate(this));
+    resize_observer_->observe(&GetVideoElement());
+  }
+
+  return HTMLDivElement::InsertedInto(root);
+}
+
 void PictureInPictureInterstitial::RemovedFrom(ContainerNode*) {
   DCHECK(!GetVideoElement().isConnected());
 
-  resize_observer_->disconnect();
-  resize_observer_.Clear();
+  if (resize_observer_) {
+    resize_observer_->disconnect();
+    resize_observer_.Clear();
+  }
 }
 
 void PictureInPictureInterstitial::NotifyElementSizeChanged(

third_party/blink/renderer/core/html/media/picture_in_picture_interstitial.h

@@ -36,6 +36,7 @@ class PictureInPictureInterstitial final : public HTMLDivElement {
   HTMLVideoElement& GetVideoElement() const { return *video_element_; }
 
   // Node override.
+  Node::InsertionNotificationRequest InsertedInto(ContainerNode*) override;
   void RemovedFrom(ContainerNode*) override;
 
   // Element: