Propagate media muted state to WebContents

Propagate media muted state to WebContents, cache it in WebContentsImpl
and make it accessible through GetMediaMuted() in C++.

BUG=729998

Change-Id: I7e6f5162db8045a02b88055ef262ec5c4e3d3913
Reviewed-on: https://chromium-review.googlesource.com/528152
Commit-Queue: Becca Hughes <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Reviewed-by: Mounir Lamouri <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#480449}
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index d683bb9..4ef2a60d 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -801,6 +801,9 @@
   // No interstitial page should already be attached.
   void AttachInterstitialPage(InterstitialPageImpl* interstitial_page) override;
 
+  void MediaMutedStatusChanged(const WebContentsObserver::MediaPlayerId& id,
+                               bool muted);
+
   // Unsets the currently showing interstitial.
   void DetachInterstitialPage() override;