Roll up patch for running layout tests under Aura.

This patch modifies RenderThemeChromiumDefault.cpp to be layout-test-aware and to match the way we draw the controls using the "mock theme" in the native-win code path. We also add a new implementation of the WebThemeEngine that draws the actual controls generically using Skia.

With this patch, we should be able to run the layout tests under Aura and everything should pass (except for the 3 tests suppressed in the TestExpectations), but there is subsequent cleanup we should do to the code to make this more generic and remove much of the testing logic from the main rendering code.

In addition, we will probably need to make a few additional changes to get this to work on Linux Aura, but not a lot.

R=jamesr@chromium.org
BUG=229207

Review URL: https://codereview.chromium.org/41733004

git-svn-id: svn://svn.chromium.org/blink/trunk@162042 bbb929c8-8fbe-4397-9dbb-9b2b20218538