Gtk: Ensure AvatarButton has pressed state when menu is showing

When using the GTK theme with --enable-native-avatar-button, it's
required that the avatar button have the pressed state when the
profile chooser menu is showing so that it looks pressed.  Previously,
the pressed state was handled by manually setting the ink drop
animation state.  Now, AvatarButton is made a sublcass of MenuButton
and reuses code from there to handle ink drop animation, and ensuring
the state becomes pressed.

Also, this incidentally fixes a bug where the ink drop would get stuck
when right clicking on the avatar button.

BUG=753067
R=msw@chromium.org
CC=sky@chromium.org

Change-Id: I6aafb5499e230859ea1ebe1c5ca6e2375ea63994
Reviewed-on: https://chromium-review.googlesource.com/744967
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513662}
4 files changed