Implement RemoteTextInputClient::ShouldDoLearning etc

Pass focus reason, client source for metrics and should do
learning on starting IME session to RemoteTextInputClient
since these should not change during an IME session;

Bug: 631527
Change-Id: I707afd9a58a29d448d497d0e0c0c19dc983cd32a
Reviewed-on: https://chromium-review.googlesource.com/c/1409917
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623793}
15 files changed