Fix a crash by search event handler for <input type=search incremental>.

Fix a crash by search event handler for <input type=search incremental>.

We had a crash in SearchInputType::didSetValueByUserEdit().

Dispatching a synchronous event here is dangerous. This CL makes the
non-standard 'search' event dispatching asynchronous in the following cases:
 - The input value becomes empty.
 - The form is submitted implicitly.
Basically 'search' event is triggered by input value changes, and is dispatched
asynchronously by a timer.  So, the behavior change should be acceptable.

BUG=570427
TEST=automated

Review URL: https://codereview.chromium.org/1529373002

Cr-Commit-Position: refs/heads/master@{#365773}
(cherry picked from commit dd6acb021e38e8181684026899fdef556099e408)

Committed: https://chromium.googlesource.com/chromium/src/+/58383a4c517b802a25ccc41b2a2219332a81e5a6

[tkent, 2015-12-21 00:50:06]

Description was changed from

==========
Fix a crash by search event handler for <input type=search incremental>.

We had a crash in SearchInputType::didSetValueByUserEdit().

Dispatching a synchronous event here is dangerous. This CL makes the
non-standard 'search' event dispatching asynchronous in the following cases:
 - The input value becomes empty.
 - The form is submitted implicitly.
Basically 'search' event is triggered by input value changes, and is dispatched
asynchronously by a timer.  So, the behavior change should be acceptable.

BUG=570427
TEST=automated

Review URL: https://codereview.chromium.org/1529373002

Cr-Commit-Position: refs/heads/master@{#365773}
(cherry picked from commit dd6acb021e38e8181684026899fdef556099e408)
==========

to

==========
Fix a crash by search event handler for <input type=search incremental>.

We had a crash in SearchInputType::didSetValueByUserEdit().

Dispatching a synchronous event here is dangerous. This CL makes the
non-standard 'search' event dispatching asynchronous in the following cases:
 - The input value becomes empty.
 - The form is submitted implicitly.
Basically 'search' event is triggered by input value changes, and is dispatched
asynchronously by a timer.  So, the behavior change should be acceptable.

BUG=570427
TEST=automated

Review URL: https://codereview.chromium.org/1529373002

Cr-Commit-Position: refs/heads/master@{#365773}
(cherry picked from commit dd6acb021e38e8181684026899fdef556099e408)

Committed:
https://chromium.googlesource.com/chromium/src/+/58383a4c517b802a25ccc41b2a22...
==========

[tkent, 2015-12-21 00:50:09]

Committed patchset #1 (id:1) manually as
58383a4c517b802a25ccc41b2a2219332a81e5a6.