Disable flaky ExtensionToolbarModelTest.SizeAfterPrefChange on Linux/Chrome OS

Disabling ExtensionToolbarModelTest.SizeAfterPrefChange due to the following
flake
../../chrome/browser/extensions/extension_toolbar_model_browsertest.cc:601: Failure
Value of: model_->GetVisibleIconCount()
  Actual: 1
  Expected: -1

BUG=379170
TBR=finnur@chromium.org,kihong.kwon@samsung.com

Review URL: https://codereview.chromium.org/308003017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274237 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/extensions/extension_toolbar_model_browsertest.cc

@@ -584,7 +584,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionToolbarModelTest, HighlightModeAdd) {
   EXPECT_EQ(id_c, ExtensionAt(2)->id());
 }
 
-IN_PROC_BROWSER_TEST_F(ExtensionToolbarModelTest, SizeAfterPrefChange) {
+// Test is flaky on Linus and ChromeOS, see crbug.com/379170.
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
+#define MAYBE_SizeAfterPrefChange DISABLED_SizeAfterPrefChange
+#else
+#define MAYBE_SizeAfterPrefChange SizeAfterPrefChange
+#endif
+IN_PROC_BROWSER_TEST_F(ExtensionToolbarModelTest, MAYBE_SizeAfterPrefChange) {
   // Load two extensions with browser action.
   base::FilePath extension_a_path(test_data_dir_.AppendASCII("api_test")
                                                 .AppendASCII("browser_action")