Browser Plugin: BrowserPluginGuest manages its own lifetime

In an effort to eventually remove BrowserPluginEmbedder, 
I've moved a guest's lifetime management to the BrowserPluginGuest itself.

1. BrowserPluginHostMsg_PluginDestroyed messages are routed to BrowserPluginGuest.
2. A guest listens for its embedder's NOTIFICATION_RENDER_VIEW_HOST_DELETED and
   destroys itself.


BUG=174673, 140316
Test=BrowserPluginHostTest.*


Review URL: https://chromiumcodereview.appspot.com/12230028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@183471 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index 279dc57..377b042 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -85,7 +85,7 @@
   WebContentsImpl* opener() const { return opener_; }
 
   // Creates a WebContents to be used as a browser plugin guest.
-  static WebContentsImpl* CreateGuest(
+  static void CreateGuest(
       BrowserContext* browser_context,
       content::SiteInstance* site_instance,
       int routing_id,