Implement Aura side of unified touch text selection for contents

This is the first part of unified touch text selection for Aura which
implements it using the new ui::TouchSelectionController for contents.

Selection updates are now coming from swap-compositor-frame IPC message
instead of selection-bounds-changed IPC message.

This CL also replaces TouchEditableImplAura (owned by
WebContentsViewAura) with ui::TouchSelectionController (owned by
RenderWidgetHostViewAura) for which a client implementation is provided
in TouchSelectionControllerClientAura.

Note that at the moment we are unable to remove selection-bounds-changed
IPC message completely as it is also used by IME and the new path is not
yet working properly inside <webview> (which is being worked on).

Next part would be using ui::TouchSelectionController to implement
unified touch text selection for Views textfields.

COLLABORATOR=mfomitchev
BUG=399721

Review URL: https://codereview.chromium.org/698253004

Cr-Commit-Position: refs/heads/master@{#341134}

0 files changed, 0 insertions, 0 deletions