Disable flaky test TopControlsManagerTest.PartialShownWithAmbiguousThresholdHides

http://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/35192/steps/cc_unittests/logs/stdio#failure1
TBR=aelias@chromium.org

BUG=456617

Review URL: https://codereview.chromium.org/913543002

Cr-Commit-Position: refs/heads/master@{#315338}

cc/input/top_controls_manager_unittest.cc

@@ -250,7 +250,7 @@ TEST(TopControlsManagerTest,
   EXPECT_FLOAT_EQ(0.f, manager->ContentTopOffset());
 }
 
-TEST(TopControlsManagerTest, PartialShownWithAmbiguousThresholdHides) {
+TEST(TopControlsManagerTest, DISABLED_PartialShownWithAmbiguousThresholdHides) {
   MockTopControlsManagerClient client(100.f, 0.25f, 0.25f);
   TopControlsManager* manager = client.manager();