Introduce a mock ui_unittests Framework for loading resources.

This allows ui_unittests to stop depending on the chrome framework.

On Mac, this creates (e.g.)
- out/ui_unittests Framework.framework/
  +-- Resources -> Versions/A/Resources
  \-- Versions
      \-- A
          \-- Resources
              +-- Info.plist
              +-- am.lproj
              |   \-- locale.pak
              +-- ...
              +-- chrome_100_percent.pak -> ui_test.pak
              +-- ...
              +-- en.lproj
              |   \-- locale.pak
              +-- ...

On other platforms, out/ui_test.pak is loaded directly and
out/ui_unittests_strings/ is set as the locale folder (for tests that
load en-US.pak from there). ui_unittests currently depends on
out/locales/ which is only created when Chrome is built.

Note that ui_unittests does not currently succeed in a clobber build
(crbug.com/347851), so that missing dependency is fixed by this change
as well.

BUG=331669, 35878, 347851
TEST=ui_unittests should build and run after clobbering the build folder

Review URL: https://codereview.chromium.org/152543005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255512 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255512