The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9bc2b7bbb5062c62fb98fb7d925765f64be80552

commit 9bc2b7bbb5062c62fb98fb7d925765f64be80552
Author: karandeepb <karandeepb@chromium.org>
Date: Wed Oct 26 06:04:30 2016

Views: Extract text selection code from Textfield.

This CL is first in part of CLs to implement text selection for Views::Labels.
This CL extracts the text selection functionality from Views::Textfield into a
new controller class called SelectionController. This class works in tandem with
its delegate. Views::Textfield implements the SelectionController::Delegate
interface.

This also fixes a couple of bugs related to middle clicks on Linux-
1) Middle clicking inside the selection region of an unfocused textfield should
   now give it focus.
2) This fixes the appearance of multiple cursors in textfields when middle
   clicking with an empty selection clipboard.

Also, Textfield now handles OnMouseCaptureLost. This ensures that the drag
selection timer is stopped and the selection clipboard is updated when mouse
capture is released.

A subsequent CL will modify views::Label to implement the
SelectionController::Delegate interface so that it also supports text selection.

Doc= https://docs.google.com/a/google.com/document/d/1JTjY8RLE84hxubCAouHuD6xVtvuMnzbqSDZyf_4N6tY/edit?usp=sharing
BUG= 630365 ,  437993 ,  657691 

Review-Url: https://codereview.chromium.org/2408623002
Cr-Commit-Position: refs/heads/master@{#427604}

[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/chrome/browser/ui/views/omnibox/omnibox_view_views.cc
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/gfx/render_text.cc
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/gfx/render_text.h
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/BUILD.gn
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/controls/textfield/textfield.cc
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/controls/textfield/textfield.h
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/controls/textfield/textfield_model.cc
[modify] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/controls/textfield/textfield_model.h
[add] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/selection_controller.cc
[add] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/selection_controller.h
[add] https://crrev.com/9bc2b7bbb5062c62fb98fb7d925765f64be80552/ui/views/selection_controller_delegate.h