Disable WebViewTest.Shim_TestAutosizeAfterNavigation on Mac because it's flaking on trybots.

BUG=326332
TBR=lazyboy@chromium.org

Review URL: https://codereview.chromium.org/103423006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239062 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239062