[Thread Safety] Replace WebString bound by cross-thread base::Bind() with base::string16

[Thread Safety] Replace WebString bound by cross-thread base::Bind() with base::string16

Passing WebString across threads is not thread-safe.

Committed: https://crrev.com/dbcc3b2ac5dcc247498eb271d10c35988a1e35a6
Cr-Commit-Position: refs/heads/master@{#341315}

[hiroshige, 2015-07-31 09:28:16]

The CQ bit was checked by hiroshige@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-07-31 09:28:41]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1257393005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1257393005/1

[commit-bot: I haz the power, 2015-07-31 10:19:42]

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

[commit-bot: I haz the power, 2015-07-31 10:19:43]

Dry run: Try jobs failed on following builders:
  win8_chromium_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_ng/...)

[hiroshige, 2015-07-31 10:27:53]

hiroshige@chromium.org changed reviewers:
+ kinuko@chromium.org

[kinuko, 2015-07-31 10:55:55]

lgtm

thanks!

[hiroshige, 2015-07-31 11:00:34]

The CQ bit was checked by hiroshige@chromium.org

[commit-bot: I haz the power, 2015-07-31 11:00:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1257393005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1257393005/1

[commit-bot: I haz the power, 2015-07-31 11:43:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-31 11:44:06]

Patchset 1 (id:??) landed as
https://crrev.com/dbcc3b2ac5dcc247498eb271d10c35988a1e35a6
Cr-Commit-Position: refs/heads/master@{#341315}