Add OnCompositionChanged and OnTextCommitted to RemoteInputMethodPrivateWin

This CL adds two new methods OnCompositionChanged and OnTextCommitted to RemoteInputMethodPrivateWin so that corresponding events occurred in the metro_driver process can be forwarded to RemoteInputMethodWin. These new methods will work as real handlelrs of MetroViewerHostMsg_ImeCompositionChanged and MetroViewerHostMsg_ImeTextCommitted messages.

In my first design, MetroViewerHostMsg_ImeCompositionChanged and MetroViewerHostMsg_ImeTextCommitted are directly handled in aura::RemoteRootWindowHostWin. However I changed my mind because how these IPC messages should be handled is a kind of implementation details of which only metro_driver::TextService implementation and ui::RemoteInputMethodWin should take care. This is why I moved these IPC handler from aura::RemoteRootWindowHostWin in ui::RemoteInputMethodPrivateWin.

BUG=164964

Review URL: https://codereview.chromium.org/85063002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237047 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237047