Re-enable CSS3DBlueBox pixel test.

Rebaselines for this test should be complete.

BUG=673752
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2588033003
Cr-Commit-Position: refs/heads/master@{#439820}

content/test/gpu/gpu_tests/pixel_expectations.py

@@ -25,11 +25,7 @@ class PixelExpectations(GpuTestExpectations):
         ['android'], bug=521588)
 
     # TODO(ccameron) fix these on Mac Retina
-    # self.Fail('Pixel_CSS3DBlueBox', ['mac'], bug=533690)
-
-    # TODO(jvanverth) remove once rebaselines are complete
-    # restore Mac-only fail above when removed
-    self.Fail('Pixel_CSS3DBlueBox', bug=673752)
+    self.Fail('Pixel_CSS3DBlueBox', ['mac'], bug=533690)
 
     # TODO(vmiura) check / generate reference images for Android devices
     self.Fail('Pixel_SolidColorBackground', ['mac', 'android'], bug=624256)