Disable WebViewTest.Shim_TestAutosizeWithPartialAttributes on Mac as well.

I saw it flake even with reruns: http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_swarming/builds/977

BUG=282116
TBR=fsamuel@chromium.org

Review URL: https://codereview.chromium.org/451183002

Cr-Commit-Position: refs/heads/master@{#288463}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288463 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/apps/web_view_browsertest.cc

@@ -853,7 +853,7 @@ IN_PROC_BROWSER_TEST_F(WebViewTest, Shim_TestAutosizeRemoveAttributes) {
 }
 
 // This test is disabled due to being flaky. http://crbug.com/282116
-#if defined(OS_WIN)
+#if defined(OS_WIN) || defined(OS_MACOSX)
 #define MAYBE_Shim_TestAutosizeWithPartialAttributes \
     DISABLED_Shim_TestAutosizeWithPartialAttributes
 #else