Get rid of FrameSelection dependency from EditorClientImpl

This patch removes FrameSelection dependency from EditorClientImpl and removes Frame.h inclusion to reduce dependency for ease of maintenance and making compilation faster.

BUG=n/a
TEST=n/a; no behavior changes

Review URL: https://codereview.chromium.org/80373002

git-svn-id: svn://svn.chromium.org/blink/trunk@162505 bbb929c8-8fbe-4397-9dbb-9b2b20218538