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- EditableTextBase's state transitions that detect insertions are unreliable:
1. when typing quickly, Chrome can and does combine events. type the keys 1, 2,
3 quickly and you might get value/text changes for "1", "12", and "123"; or you
might get value changes for "1", "123". The latter is really bad and triggers
the insertion (with length > 1) state erroniously.
2. the source of the insertion is unclear. It might have been from a paste, programmatic splicing.
3. It is impossible to reconstruct what part of the text actually got
inserted. Trivial example: 'aaa', 'aaaaaaaa'. Unknown whether the entire value was replaced, or just a substring.

In this change, we will turn off insertion announcements, which were being
triggered in many undesirable code paths.

Instead, we will:
- listen to clipboard events for cut, copy, paste (and
remove the previous copy command)
- fixes the regression introduced by splitting
text field into several subroles. Set selection wasn't working.

Test: type a lot with various typing echo settings and cut/copy/paste.

Bug: 791157
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ida442aa0656c1d66e489c6064f8959ccb7177b46
Reviewed-on: https://chromium-review.googlesource.com/804535
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521793}