[chromium] Enable more of webkit_unit_tests in component builds
https://bugs.webkit.org/show_bug.cgi?id=109369

Reviewed by Darin Fisher.

Add a set of testing APIs to a WebUnitTestSupport interface available off of Platform for unit tests to access
in component builds.

* chromium/public/Platform.h:
(WebKit):
(Platform):
(WebKit::Platform::unitTestSupport):
* chromium/public/WebUnitTestSupport.h: Added.
(WebKit):
(WebUnitTestSupport):
(WebKit::WebUnitTestSupport::registerMockedURL):
(WebKit::WebUnitTestSupport::registerMockedErrorURL):
(WebKit::WebUnitTestSupport::unregisterMockedURL):
(WebKit::WebUnitTestSupport::unregisterAllMockedURLs):
(WebKit::WebUnitTestSupport::serveAsynchronousMockedRequests):
(WebKit::WebUnitTestSupport::webKitRootDir):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142388 268f45cc-cd09-0410-ab3c-d52691b4dbfc