Marking ExternalTabUITest, TabPostMessage as flaky.

BUG=44617
TEST=none
TBR=cbentzel,stoyan

Review URL: http://codereview.chromium.org/2135008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@47758 0039d316-1c4b-4281-b951-d872f2087c98

chrome/test/automation/automation_proxy_uitest.cc

@@ -926,7 +926,8 @@ TEST_F(ExternalTabUITest, IncognitoMode) {
   tab = NULL;
 }
 
-TEST_F(ExternalTabUITest, TabPostMessage) {
+// FLAKY: http://crbug.com/44617
+TEST_F(ExternalTabUITest, FLAKY_TabPostMessage) {
   scoped_refptr<TabProxy> tab;
   TimedMessageLoopRunner loop(MessageLoop::current());
   ASSERT_THAT(mock_, testing::NotNull());