Disable SyntheticKeyEventTest.KeyboardEventAck

It's flaky everywhere, not just mash.

TBR=caseq@chromium.org

Bug: 889878
Change-Id: Iae5bdc6625102ad5dc59707a68f1f67db2a53dcd
Reviewed-on: https://chromium-review.googlesource.com/c/1318801Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605755}

content/browser/devtools/protocol/devtools_protocol_browsertest.cc

@@ -243,7 +243,8 @@ IN_PROC_BROWSER_TEST_F(SyntheticKeyEventTest, KeyEventSynthesizeKey) {
   EXPECT_EQ("\"Escape\"", key);
 }
 
-IN_PROC_BROWSER_TEST_F(SyntheticKeyEventTest, KeyboardEventAck) {
+// Flaky: https://crbug.com/889878
+IN_PROC_BROWSER_TEST_F(SyntheticKeyEventTest, DISABLED_KeyboardEventAck) {
   NavigateToURLBlockUntilNavigationsComplete(shell(), GURL("about:blank"), 1);
   Attach();
   ASSERT_TRUE(content::ExecuteScript(

testing/buildbot/filters/chromeos.single_process_mash.content_browsertests.filter

@@ -19,7 +19,3 @@
 # or RenderWidgetHostMouseEventMonitor::EventWasReceived fails.
 # https://crbug.com/884360
 -SitePerProcessHitTestBrowserTest.CrossProcessTooltipTest*
-
-
-# Flaky. https://crbug.com/889878
--SyntheticKeyEventTest.KeyboardEventAck