Merge to m56: Fix issues with sending tts queue lots of utterances

Merge to m56: Fix issues with sending tts queue lots of utterances

- $descendants for div's can be very expensive. For example, in Gmail, there is a focusable div that wraps almost the entire contents of the page. We end up generating Output for everything under the div and lag significantly when focus lands here.
Fix this by only taking the text content of divs as one large string.  $descendants had all output including rich formatting.
- live region output on alerts causes double output (and similar lag). For example, pressing '?' in Gmail triggers hundreds of runs inside of LiveRegion.
Fix this by ignoring live regions set on alert nodes.

TEST=navigate in Gmail.
BUG=672955
TBR=dtseng@chromium.org

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2563173002
Cr-Commit-Position: refs/heads/master@{#437925}
(cherry picked from commit a740f7ec72a6bf88e269f52c5561dd57ffde1589)

Committed: https://chromium.googlesource.com/chromium/src/+/d0f1e3d1b5534b5b963f26f4e9e096ef3bc44bee

[David Tseng, 2016-12-13 23:45:46]

Description was changed from

==========
Merge to m56: Fix issues with sending tts queue lots of utterances

- $descendants for div's can be very expensive. For example, in Gmail, there is
a focusable div that wraps almost the entire contents of the page. We end up
generating Output for everything under the div and lag significantly when focus
lands here.
Fix this by only taking the text content of divs as one large string. 
$descendants had all output including rich formatting.
- live region output on alerts causes double output (and similar lag). For
example, pressing '?' in Gmail triggers hundreds of runs inside of LiveRegion.
Fix this by ignoring live regions set on alert nodes.

TEST=navigate in Gmail.
BUG=672955
TBR=dtseng@chromium.org

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2563173002
Cr-Commit-Position: refs/heads/master@{#437925}
(cherry picked from commit a740f7ec72a6bf88e269f52c5561dd57ffde1589)
==========

to

==========
Merge to m56: Fix issues with sending tts queue lots of utterances

- $descendants for div's can be very expensive. For example, in Gmail, there is
a focusable div that wraps almost the entire contents of the page. We end up
generating Output for everything under the div and lag significantly when focus
lands here.
Fix this by only taking the text content of divs as one large string. 
$descendants had all output including rich formatting.
- live region output on alerts causes double output (and similar lag). For
example, pressing '?' in Gmail triggers hundreds of runs inside of LiveRegion.
Fix this by ignoring live regions set on alert nodes.

TEST=navigate in Gmail.
BUG=672955
TBR=dtseng@chromium.org

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2563173002
Cr-Commit-Position: refs/heads/master@{#437925}
(cherry picked from commit a740f7ec72a6bf88e269f52c5561dd57ffde1589)

Committed:
https://chromium.googlesource.com/chromium/src/+/d0f1e3d1b5534b5b963f26f4e9e0...
==========

[David Tseng, 2016-12-13 23:45:47]

Committed patchset #1 (id:1) manually as
d0f1e3d1b5534b5b963f26f4e9e096ef3bc44bee (presubmit successful).