Remove most ScopedVector usage from c/b/extensions.

Replace them with vector<unique_ptr<T>>.

After this CL there will be only 3 places where ScopedVector
would still be around. Since those (language_settings_private_delegate.cc,
web_navigation_apitest.cc and chrome_content_browser_client_extensions_part.cc)
are non-trivial, I will try to remove ScopedVector from them in subsequent CLs.

BUG=556939
Test=None, internal only change.

Review-Url: https://codereview.chromium.org/2310683002
Cr-Commit-Position: refs/heads/master@{#417042}
40 files changed