Use FrameMatchingPredicate() to find RenderFrameHosts in ExtensionWebUITest.

Use FrameMatchingPredicate() to find RenderFrameHosts in ExtensionWebUITest.

When looking for a RFH by last committed URL, there is no need to do a ForEach with a private FindFrame() predicate, since that logic is already available from a public FrameMatchingPredicate method in browser_test_utils.

BUG=

Committed: https://crrev.com/c515c08b4d0b62a3b24540b6c2fd6db86fdfa250
Cr-Commit-Position: refs/heads/master@{#308458}

[alexmos, 2014-12-15 21:53:14]

alexmos@chromium.org changed reviewers:
+ asargent@chromium.org

[alexmos, 2014-12-15 21:53:14]

asargent@, could you please review this CL?  I was working on another CL, and
this FindFrame code confused me about how to best find RenderFrameHosts by URL,
so I wanted to clean it up to be consistent everywhere.

[asargent_no_longer_on_chrome, 2014-12-15 22:49:42]

lgtm

[alexmos, 2014-12-15 22:52:50]

The CQ bit was checked by alexmos@chromium.org

[commit-bot: I haz the power, 2014-12-15 22:53:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/807463003/1

[commit-bot: I haz the power, 2014-12-15 23:33:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-15 23:34:02]

Patchset 1 (id:??) landed as
https://crrev.com/c515c08b4d0b62a3b24540b6c2fd6db86fdfa250
Cr-Commit-Position: refs/heads/master@{#308458}