Don't run ChromePluginTest.InstalledPlugins in is_official_build=true...

Don't run ChromePluginTest.InstalledPlugins in is_official_build=true is_chrome_branded=false builds.

ToTWinLibcxx64 sets is_official_build=true but doesn't have src-internal
checked out.  The test currently fails there because it needs files from
src-internal.  The fix is to run the test if is_chrome_branded is set (which
requires a src-internal checkout), instead of when is_official_build is set.

Bug: 801780
Change-Id: Icbfaf8c978ac7618d67b1d7e0cd1f48be45a8232
Reviewed-on: https://chromium-review.googlesource.com/957123Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542098}

chrome/browser/chrome_plugin_browsertest.cc

@@ -214,7 +214,7 @@ IN_PROC_BROWSER_TEST_F(ChromePluginTest, DISABLED_Flash) {
   EnsureFlashProcessCount(1);
 }
 
-#if defined(OFFICIAL_BUILD)
+#if defined(GOOGLE_CHROME_BUILD)
 // Verify that the official builds have the known set of plugins.
 IN_PROC_BROWSER_TEST_F(ChromePluginTest, InstalledPlugins) {
   const char* expected[] = {