Disable AppWindowApiTest.Get as it's semi-consistently failing on Linux

CFI bots and some Windows/ChromeOS try jobs.

R=jbudorick@chromium.org
TBR=tapted@chromium.org
BUG=978272

Change-Id: I8012213fc915b8e8aef7457d8c25ecd6fab7bd48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674711
Commit-Queue: Dan Beam <dbeam@chromium.org>
Auto-Submit: Dan Beam <dbeam@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671924}

extensions/browser/api/app_window/app_window_apitest.cc

@@ -117,7 +117,9 @@ IN_PROC_BROWSER_TEST_F(AppWindowApiTest, AlwaysOnTopNoPermissions) {
       "platform_apps/windows_api_always_on_top/no_permissions")) << message_;
 }
 
-IN_PROC_BROWSER_TEST_F(AppWindowApiTest, Get) {
+// https://crbug.com/978272 - semi-consistently timing out on Linux CFI bots,
+// and flaking in some Windows/ChromeOS try runs.
+IN_PROC_BROWSER_TEST_F(AppWindowApiTest, DISABLED_Get) {
   EXPECT_TRUE(RunPlatformAppTest("platform_apps/windows_api_get"))
       << message_;
 }