Keep lock during all of ScriptStreamer::fetchDataFromResourceBuffer.

Keep lock during all of ScriptStreamer::fetchDataFromResourceBuffer.

This fixes a race condition where both the main thread and the V8 background
parsing thread call fetchDataFromResourceBuffer. The current lock makes sure
only one thread will fetch data from teh resourceBuffer at a time, and the
queue they put it in is natively thread safe, but - if threads race in just
the right way - the order might be reversed.

Example:
- thread 1 acquires lock, fetches data from resource buffer.
- thread 1 gets interruped; new data arrives in the resource buffer.
- thread 2 acquires lock, fetches data from resource buffer
- thread 2 adds its chunks to the data queue
- thread 1 adds its chunks to the data queue
-> the chunks are now queued in the wrong order.

BUG=510825
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200990

[vogelheim, 2015-08-20 13:31:52]

vogelheim@chromium.org changed reviewers:
+ mkwst@chromium.org

[vogelheim, 2015-08-20 13:31:52]

Hi Mike, please review whenever it's convenient. The "usual suspects" are OoO
for ~2 weeks.

If you need more info: The whole drama is documenteds in the linked issue,
including a description of why I think this is right.

[Mike West, 2015-08-20 17:02:38]

On 2015/08/20 at 13:31:52, vogelheim wrote:
> Hi Mike, please review whenever it's convenient. The "usual suspects" are OoO
for ~2 weeks.
> 
> If you need more info: The whole drama is documenteds in the linked issue,
including a description of why I think this is right.

I think so too. Thanks for the pointers to documentation. LGTM.

[vogelheim, 2015-08-21 08:26:19]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2015-08-21 08:26:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1286883004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1286883004/1

[commit-bot: I haz the power, 2015-08-21 14:27:23]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-21 14:27:24]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[vogelheim, 2015-08-21 16:42:03]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2015-08-21 16:42:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1286883004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1286883004/1

[commit-bot: I haz the power, 2015-08-21 16:46:51]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200990