Fix logic handling empty strings in tts.

Fix logic handling empty strings in tts.

Previously, we explicitly stopped speech when encountering a call to speak only whitespace. However, since sometimes we get whitespace from an unreliable source, it can actually cause other utterances to be interrupted.

One such example is Sheets. When arrowing around, we observe some events resulting in empty speech which interrupts cell announcement.

Committed: https://crrev.com/112cdcfa70a21b026abe0228c9b5ebb2fb287a3e
Cr-Commit-Position: refs/heads/master@{#379308}

[David Tseng, 2016-03-03 22:13:33]

Description was changed from

==========
Fix logic handling empty strings in tts.
==========

to

==========
Fix logic handling empty strings in tts.

Previously, we explicitly stopped speech when encountering a call to speak only
whitespace. However, since sometimes we get whitespace from an unreliable
source, it can actually cause other utterances to be interrupted.

One such example is Sheets. When arrowing around, we observe some events
resulting in empty speech which interrupts cell announcement.
==========

[David Tseng, 2016-03-03 22:13:33]

dtseng@chromium.org changed reviewers:
+ dmazzoni@chromium.org

[dmazzoni, 2016-03-03 23:51:54]

lgtm

[David Tseng, 2016-03-04 17:04:21]

The CQ bit was checked by dtseng@chromium.org

[commit-bot: I haz the power, 2016-03-04 17:04:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1762843002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1762843002/1

[commit-bot: I haz the power, 2016-03-04 17:51:38]

Description was changed from

==========
Fix logic handling empty strings in tts.

Previously, we explicitly stopped speech when encountering a call to speak only
whitespace. However, since sometimes we get whitespace from an unreliable
source, it can actually cause other utterances to be interrupted.

One such example is Sheets. When arrowing around, we observe some events
resulting in empty speech which interrupts cell announcement.
==========

to

==========
Fix logic handling empty strings in tts.

Previously, we explicitly stopped speech when encountering a call to speak only
whitespace. However, since sometimes we get whitespace from an unreliable
source, it can actually cause other utterances to be interrupted.

One such example is Sheets. When arrowing around, we observe some events
resulting in empty speech which interrupts cell announcement.
==========

[commit-bot: I haz the power, 2016-03-04 17:51:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-04 17:53:32]

Description was changed from

==========
Fix logic handling empty strings in tts.

Previously, we explicitly stopped speech when encountering a call to speak only
whitespace. However, since sometimes we get whitespace from an unreliable
source, it can actually cause other utterances to be interrupted.

One such example is Sheets. When arrowing around, we observe some events
resulting in empty speech which interrupts cell announcement.
==========

to

==========
Fix logic handling empty strings in tts.

Previously, we explicitly stopped speech when encountering a call to speak only
whitespace. However, since sometimes we get whitespace from an unreliable
source, it can actually cause other utterances to be interrupted.

One such example is Sheets. When arrowing around, we observe some events
resulting in empty speech which interrupts cell announcement.

Committed: https://crrev.com/112cdcfa70a21b026abe0228c9b5ebb2fb287a3e
Cr-Commit-Position: refs/heads/master@{#379308}
==========

[commit-bot: I haz the power, 2016-03-04 17:53:33]

Patchset 1 (id:??) landed as
https://crrev.com/112cdcfa70a21b026abe0228c9b5ebb2fb287a3e
Cr-Commit-Position: refs/heads/master@{#379308}

[David Tseng, 2016-03-08 20:13:59]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1770943004/ by dtseng@chromium.org.

The reason for reverting is: It turns out this causes Output.flushNextUtterance
to not get applied correctly. Output sometimes sends an empty string as its
first utterance..