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This follows the rule we setup for //ui which states that each subdir
should be its own component with its own gyp file that lives in its
subdir.

The 'ui' target was renamed to ui_base to match the convention.

BUG=299841
TEST=gyp files.
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/198333004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256788 0039d316-1c4b-4281-b951-d872f2087c98