Explicitly pass WebString to enableFeatureFromString()

Explicitly pass WebString to enableFeatureFromString()

We are going to replace WebString with std::string in WebRuntimeFeatures[1].
As a preparation, this CL passes WebString object to enableFeatureFromString()
explicitly because we will add another enableFeatureFromString() which takes
std::string, which will be ambiguous if we pass string literal. I'll revert
this CL when blink side CL is landed.

[1] https://codereview.chromium.org/1259763006/

BUG=501171
Committed: https://crrev.com/31ad3e6a80c367c4f8ea0a921e8f2cfe555a5fd6
Cr-Commit-Position: refs/heads/master@{#341690}

[bashi, 2015-08-04 00:27:29]

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

[bashi, 2015-08-04 00:27:30]

Kinuko-san, could you review this trivial one?

I needed this CL to land https://codereview.chromium.org/1259763006/

[haraken, 2015-08-04 00:28:28]

non-owner LGTM

[kinuko, 2015-08-04 04:38:18]

lgtm

[bashi, 2015-08-04 04:40:44]

The CQ bit was checked by bashi@chromium.org

[commit-bot: I haz the power, 2015-08-04 04:41:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1269793007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1269793007/1

[commit-bot: I haz the power, 2015-08-04 06:16:52]

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

[commit-bot: I haz the power, 2015-08-04 06:16:52]

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

[bashi, 2015-08-04 06:18:00]

The CQ bit was checked by bashi@chromium.org

[commit-bot: I haz the power, 2015-08-04 06:18:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1269793007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1269793007/1

[commit-bot: I haz the power, 2015-08-04 07:01:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-04 07:02:32]

Patchset 1 (id:??) landed as
https://crrev.com/31ad3e6a80c367c4f8ea0a921e8f2cfe555a5fd6
Cr-Commit-Position: refs/heads/master@{#341690}