Introduce ScopedViewsTestHelper to run App Info dialog unittests on Mac
Follow-up to http://crrev.com/334533 which decoupled the ash-specific
test.
The remaining tests have both an Extensions and a Views dependency. The
extension system requires a BrowserThreadBundle (from content), which
was previously provided by AshTestBase. However, ViewsTestBase does not
(and shouldn't) have a content dependency. Instead, use the
BrowserThreadBundle provided by TestExtensionEnvironment which has some
other useful things.
Then, to satisfy the Views dependency, we still can't use ViewsTestBase
because it has its own MessageLoop that will fight with the
BrowserThreadBundle. Use ViewsTestHelper. But this is a bit fiddly.
Rather than copy-pasting some boilerplate, make `ScopedViewsTestHelper`
to encapsulate the compositor, views delegate, and input method
initialization from ViewsTestBase into ScopedViewsTestHelper.
Another test harness had the same problem. That is, wanting a
BrowserThreadBundle and so being unable to use ViewsTestBase. So
collapse some boilerplate in DesktopMediaPickerViewsTest as well.
BUG=485854, 412234
Review URL: https://codereview.chromium.org/
1184093010
Cr-Commit-Position: refs/heads/master@{#334800}