Expand suspension of idle media players to all platforms.

media/blink/webmediaplayer_delegate.h

Index: media/blink/webmediaplayer_delegate.h
diff --git a/media/blink/webmediaplayer_delegate.h b/media/blink/webmediaplayer_delegate.h
index 7ae31df780b888b8248e41d92e5fd338a3c35e23..2e6f8915f8d7d108d64ecb4f629677f4be762c6c 100644
--- a/media/blink/webmediaplayer_delegate.h
+++ b/media/blink/webmediaplayer_delegate.h
@@ -16,11 +16,17 @@ class WebMediaPlayerDelegate {
  public:
   class Observer {
    public:
-    // Called when the WebMediaPlayer is no longer in the foreground.  Audio may
-    // continue in the background unless |must_suspend| is true.
-    virtual void OnHidden(bool must_suspend) = 0;
-
+    // Called when the WebMediaPlayer enters the background or foreground
+    // respectively.
+    virtual void OnHidden() = 0;
     virtual void OnShown() = 0;
+
+    // Called when a WebMediaPlayer instance is asked to release any held
+    // resources.  If |must_suspend| is false, the player may continue to play
+    // background audio.  If |must_suspend| is true, after releasing resources,
+    // players must call WebMediaPlayerDelegate::PlayerGone().

[xhwang, 2016/03/07 19:13:58]

It seems PlayerGone() may also be called in OnHidden() or OnSuspend(false). We
should make this more clear.

[DaleCurtis, 2016/03/09 02:56:13]

Done.

+    virtual void OnSuspend(bool must_suspend) = 0;

[xhwang, 2016/03/07 19:13:58]

It seems there's some overlap between OnHidden() and OnSuspend(). For example,
when a player enters background and we want to suspend video but keep playing
background audio, should we call OnHidden(), or OnSuspend(false)?

[DaleCurtis, 2016/03/07 19:23:07]

With this change OnHidden() should only ever be called for transitions into the
background. Likewise, OnSuspend() will be called only in cases where we're
requesting suspend for release of idle resources or requiring suspend for a
pending undoable tab closure.

sandersd@ suggested some time ago that instead of having a bool we have an enum
like

SuspendReason { OPTIONAL_FOR_IDLE_RESOURCES, MANDATORY_FOR_PENDING_DESTRUCTION }

I couldn't come up with good names so I kept the bool instead, but I'm open to
suggestions :)

+
     virtual void OnPlay() = 0;
     virtual void OnPause() = 0;