Make BrowserMessageFilter not derive from IPC::ChannelProxy::MessageFilter. This allows us to hide the OnMessageReceived which shouldn't be overridden from child classes, and also avoid the pattern of requiring an overridden method to have to call to the base class.

R=scherkus@chromium.org, scherkus

Review URL: https://codereview.chromium.org/24514003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226251 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226251