blink:bindings: Passes the global context instead of |this| in JS.

blink:bindings: Passes the global context instead of |this| in JS.

|this| in JS (args.Holder() in C++ code) is not a reliable object.  User
script can pass any object as |this|.  So we shouldn't use it as creation
context when calling Blink APIs to create a new DOM wrapper.

We should instead use the current context where the user script is running
as creation context.

BUG=497507
Committed: https://crrev.com/42bd05a2bf4260f500687a2457d01e298033f2bb
Cr-Commit-Position: refs/heads/master@{#334366}

[Yuki, 2015-06-12 07:30:35]

yukishiino@chromium.org changed reviewers:
+ kalman@chromium.org

[Yuki, 2015-06-12 07:30:36]

kalman, could you review this CL as an owner of chrome/renderer/extensions/ and
extensions/ ?

[haraken, 2015-06-12 07:34:25]

non-owner LGTM

[not at google - send to devlin, 2015-06-12 16:01:27]

lgtm

[Yuki, 2015-06-15 06:06:08]

The CQ bit was checked by yukishiino@chromium.org

[commit-bot: I haz the power, 2015-06-15 06:06:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1174343003/1

[commit-bot: I haz the power, 2015-06-15 08:17:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-15 08:18:37]

Patchset 1 (id:??) landed as
https://crrev.com/42bd05a2bf4260f500687a2457d01e298033f2bb
Cr-Commit-Position: refs/heads/master@{#334366}