Route ExtendSelectionAndDelete to active text widget

It seems that RenderWidgetHostViewAura::ExtendSelectionAndDelete fails
to respect the active widget of the TextInputManager, and since different
widgets can have completely separate FrameTrees, getting the correct
focused frame relies on routing to the active widget.

Bug: 971985
Change-Id: I4bf5e21b8d928692a64315fe71a43ea5d874102b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1692877
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676999}
6 files changed