Fix extension bindings injection for iframes

Fix extension bindings injection for iframes

For iframes, we don't want to use the source url for determining the
associated extension because it starts out with an about:blank context
that is scriptable by its parent.

BUG=573131
Review-Url: https://codereview.chromium.org/2151693002
Cr-Commit-Position: refs/heads/master@{#407214}
(cherry picked from commit 91f655b19888da3f86b57ad8c548da93e7b9aba4)

Committed: https://chromium.googlesource.com/chromium/src/+/d578daf3167747cbfe89cba4c4ca70a88e78651a

[asargent_no_longer_on_chrome, 2016-07-25 17:46:46]

Description was changed from

==========
Fix extension bindings injection for iframes

For iframes, we don't want to use the source url for determining the
associated extension because it starts out with an about:blank context
that is scriptable by its parent.

BUG=573131

Review-Url: https://codereview.chromium.org/2151693002
Cr-Commit-Position: refs/heads/master@{#407214}
(cherry picked from commit 91f655b19888da3f86b57ad8c548da93e7b9aba4)
==========

to

==========
Fix extension bindings injection for iframes

For iframes, we don't want to use the source url for determining the
associated extension because it starts out with an about:blank context
that is scriptable by its parent.

BUG=573131

Review-Url: https://codereview.chromium.org/2151693002
Cr-Commit-Position: refs/heads/master@{#407214}
(cherry picked from commit 91f655b19888da3f86b57ad8c548da93e7b9aba4)

Committed:
https://chromium.googlesource.com/chromium/src/+/d578daf3167747cbfe89cba4c4ca...
==========

[asargent_no_longer_on_chrome, 2016-07-25 17:46:47]

Committed patchset #1 (id:1) manually as
d578daf3167747cbfe89cba4c4ca70a88e78651a.