Detect change on the intersection of video and viewport.

media/base/media_observer.h

Index: media/base/media_observer.h
diff --git a/media/base/media_observer.h b/media/base/media_observer.h
index c3e29a1789f173d2cc62ad12845392cfaf1a70f7..edf43b464e54f9418ab3a7a718158d11f4c1b799 100644
--- a/media/base/media_observer.h
+++ b/media/base/media_observer.h
@@ -7,6 +7,7 @@
 
 #include "media/base/cdm_context.h"
 #include "media/base/pipeline_metadata.h"
+#include "ui/gfx/geometry/rect.h"
 
 namespace media {
 
@@ -16,10 +17,22 @@ class MEDIA_EXPORT MediaObserver {
   MediaObserver();
   virtual ~MediaObserver();
 
+  struct ViewportIntersectionInfo {
+    ViewportIntersectionInfo() {}
+    ~ViewportIntersectionInfo() {}
+
+    gfx::Rect root_rect;
+    gfx::Rect intersect_rect;
+  };
+
   // Called when the media element entered/exited fullscreen.
   virtual void OnEnteredFullscreen() = 0;
   virtual void OnExitedFullscreen() = 0;
 
+  // Called when the intersection of the video element and viewport changes.
+  virtual void OnVideoViewportIntersectionChanged(

[miu, 2016/11/21 21:07:03]

naming nit: Just OnViewportIntersectionChanged (no "video" at front) because
this could be called by any type of media element (not just video). (and please
adjust code comment)

[xjz, 2016/11/21 23:58:42]

Done.

+      const ViewportIntersectionInfo& info) {}
+
   // Called when CDM is attached to the media element. The |cdm_context| is
   // only guaranteed to be valid in this call.
   virtual void OnSetCdm(CdmContext* cdm_context) = 0;