Disable CrExtensionsToolbarTest.ClickHandlers on non-macos

Disabling this test as it regularly (~50% of times) times out on Linux and
Windows. The test is fine on MacOS.

TBR=rdevlin.cronin@chromium.org

Bug: 882342
Change-Id: I23dd794332f57cbbd46ba167efc562041f7e9dff
Reviewed-on: https://chromium-review.googlesource.com/1215284Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589862}

chrome/test/data/webui/extensions/cr_extensions_browsertest.js

@@ -121,7 +121,13 @@ TEST_F('CrExtensionsToolbarTest', 'DevModeToggle', function() {
   this.runMochaTest(extension_toolbar_tests.TestNames.DevModeToggle);
 });
 
-TEST_F('CrExtensionsToolbarTest', 'ClickHandlers', function() {
+// TODO(crbug.com/882342) Disabled on other platforms but MacOS due to timeouts.
+GEN('#if !defined(OS_MACOSX)');
+GEN('#define MAYBE_ClickHandlers DISABLED_ClickHandlers');
+GEN('#else');
+GEN('#define MAYBE_ClickHandlers ClickHandlers');
+GEN('#endif');
+TEST_F('CrExtensionsToolbarTest', 'MAYBE_ClickHandlers', function() {
   this.runMochaTest(extension_toolbar_tests.TestNames.ClickHandlers);
 });