Add target for webkit_compositor_unittests

We need a target for unit tests that test the compositor WebKit APIs but have
knowledge of the implementation (CC guts). This sets up the test target and
puts a few tests in place. Like cc_unittests, this target doesn't work in the
component build and won't until we break link-time dependencies on non-exported
WebCore symbols.

BUG=

Review URL: https://chromiumcodereview.appspot.com/10874095

git-svn-id: http://src.chromium.org/svn/trunk/src/build@153798 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

all.gyp

@@ -65,6 +65,7 @@
             '../third_party/WebKit/Source/WebKit/chromium/All.gyp:*',
             '../third_party/WebKit/Source/WebKit/chromium/WebKit.gyp:generate_devtools_zip',
             '../v8/tools/gyp/v8.gyp:*',
+            '../webkit/compositor/compositor_tests.gyp:*',
             '../webkit/support/webkit_support.gyp:*',
             '../webkit/webkit.gyp:*',
             '<(libjpeg_gyp_path):*',