Provide a WebContents API to discover the playback of a fullscreen video.

content/browser/media/media_web_contents_observer.h

Index: content/browser/media/media_web_contents_observer.h
diff --git a/content/browser/media/media_web_contents_observer.h b/content/browser/media/media_web_contents_observer.h
index 5d6d8d2f5ff92d2f54f53bafcd1e03aa7642cab7..2a37a08d50359fe1118c2c5813331607298423f0 100644
--- a/content/browser/media/media_web_contents_observer.h
+++ b/content/browser/media/media_web_contents_observer.h
@@ -42,6 +42,11 @@ class CONTENT_EXPORT MediaWebContentsObserver : public WebContentsObserver {
   // Called by WebContentsImpl when the audible state may have changed.
   void MaybeUpdateAudibleState();
 
+  // Called by WebContentsImpl to know if an active player is currently
+  // fullscreen dominant.
+  // It should only be called while the WebContents is fullscreen.
+  bool HasActiveFullscreenDominantVideo() const;

[liberato (no reviews please), 2017/02/14 23:00:01]

naming is a little confusing.

personally, i'd go more for something like this:

- remove 'dominant' from the name - maybe HasActiveEffectivelyFullscreenVideo()
or similar.
- returns 'no' if webcontents isn't full screen, rather than dcheck.

otherwise, 'dominant' and/or 'fullscreen' seem overloaded.

as in, the caller wants to know 'is the user looking at a really big video in
this webcontents right now?'

[mlamouri (slow - plz ping), 2017/02/17 16:36:24]

Renamed to `HasActiveEffectivelyFullscreenVideo`. It's quite better :)

+
   // WebContentsObserver implementation.
   void WebContentsDestroyed() override;
   void RenderFrameDeleted(RenderFrameHost* render_frame_host) override;
@@ -74,6 +79,12 @@ class CONTENT_EXPORT MediaWebContentsObserver : public WebContentsObserver {
                       bool has_audio,
                       bool is_remote,
                       media::MediaContentType media_content_type);
+  void OnMediaFullscreenChange(RenderFrameHost* render_frame_host,
+                               int delegate_id,
+                               bool is_fullscreen);
+  void OnMediaDominantChange(RenderFrameHost* render_frame_host,
+                             int delegate_id,
+                             bool is_dominant);
 
   // Clear |render_frame_host|'s tracking entry for its power save blockers.
   void ClearPowerSaveBlockers(RenderFrameHost* render_frame_host);
@@ -107,6 +118,25 @@ class CONTENT_EXPORT MediaWebContentsObserver : public WebContentsObserver {
   std::unique_ptr<device::PowerSaveBlocker> audio_power_save_blocker_;
   std::unique_ptr<device::PowerSaveBlocker> video_power_save_blocker_;
 
+  // FullscreenDominantInfo keeps track of whether a MediaPlayerId is fullscreen
+  // or dominant inside a fullscreen frame.
+  struct FullscreenDominantInfo {
+    FullscreenDominantInfo() = delete;
+    FullscreenDominantInfo(const FullscreenDominantInfo&) = default;
+    FullscreenDominantInfo& operator=(const FullscreenDominantInfo&) = default;
+
+    FullscreenDominantInfo(bool fullscreen, bool dominant)
+        : fullscreen(fullscreen), dominant(dominant) {}
+
+    bool fullscreen = false;
+    bool dominant = false;
+  };
+
+  // If the |MediaPlayerId| is set to |{ nullptr, 0 }|, |FullscreenDominantInfo|
+  // should be ignored.
+  std::pair<MediaPlayerId, FullscreenDominantInfo> fullscreen_dominant_video_ =

[liberato (no reviews please), 2017/02/14 23:00:01]

nit: perhaps move MediaPlayerId into FullscreenDominantInfo.  all of the
'.first.first' are a bit confusing.

[mlamouri (slow - plz ping), 2017/02/17 16:36:24]

I switched to base::Optional<MediaPlayerId>. Should be simpler :)

+      {{nullptr, 0}, FullscreenDominantInfo(false, false)};
+
   MediaSessionControllersManager session_controllers_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaWebContentsObserver);