Remove unnecessary SupportsWeakPtr base from ChromotingInstance.

remoting/client/plugin/chromoting_instance.h

Index: remoting/client/plugin/chromoting_instance.h
diff --git a/remoting/client/plugin/chromoting_instance.h b/remoting/client/plugin/chromoting_instance.h
index b98d922fb6e8411e77d9e6a6a146d093ff9a725b..d7fd4481f342221ea8701f1a9966186c6f7b874e 100644
--- a/remoting/client/plugin/chromoting_instance.h
+++ b/remoting/client/plugin/chromoting_instance.h
@@ -71,8 +71,7 @@ class ChromotingInstance :
       public ClientUserInterface,
       public protocol::ClipboardStub,
       public protocol::CursorShapeStub,
-      public pp::Instance,
-      public base::SupportsWeakPtr<ChromotingInstance> {
+      public pp::Instance {
  public:
   // Plugin API version. This should be incremented whenever the API
   // interface changes.
@@ -258,6 +257,7 @@ class ChromotingInstance :
 
   base::WeakPtr<PepperTokenFetcher> pepper_token_fetcher_;
 
+  // Weak reference to this instance, used for global logging and task posting.
   base::WeakPtrFactory<ChromotingInstance> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromotingInstance);