Disable flaky ChromePluginTest.InstalledPlugins on ChromeOS.

It is flaky:
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome

We should use async semantics rather than wait runloop at GetPlugins().

TBR=sky@chromium.org
BUG=1147726

Change-Id: I003bee856004e0f7476cf008429d68284776173f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2531418Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826145}

chrome/browser/chrome_plugin_browsertest.cc

@@ -48,7 +48,12 @@ std::vector<content::WebPluginInfo> GetPlugins() {
 using ChromePluginTest = InProcessBrowserTest;
 
 // Verify that the official builds have the known set of plugins.
-IN_PROC_BROWSER_TEST_F(ChromePluginTest, InstalledPlugins) {
+#if defined(OS_CHROMEOS) // http://crbug.com/1147726
+#define MAYBE_InstalledPlugins DISABLED_InstalledPlugins
+#else
+#define MAYBE_InstalledPlugins InstalledPlugins
+#endif
+IN_PROC_BROWSER_TEST_F(ChromePluginTest, MAYBE_InstalledPlugins) {
   const char* expected[] = {
       "Chrome PDF Plugin",
       "Native Client",