Revert of Moves ash content specific tests into ash_content_unittests

ash/test/ash_test_base.h

Index: ash/test/ash_test_base.h
diff --git a/ash/test/ash_test_base.h b/ash/test/ash_test_base.h
index 8e11877c3363689b984cff198d7c860053a0e68f..63e1cf8fe979763e0bb6ccdecb77bf8134244dcc 100644
--- a/ash/test/ash_test_base.h
+++ b/ash/test/ash_test_base.h
@@ -15,6 +15,7 @@
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/threading/thread.h"
+#include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/display/display.h"
@@ -52,10 +53,12 @@
 
 namespace test {
 
-class AshTestEnvironment;
 class AshTestHelper;
 class TestScreenshotDelegate;
 class TestSystemTrayDelegate;
+#if defined(OS_WIN)
+class TestMetroViewerProcessHost;
+#endif
 
 class AshTestBase : public testing::Test {
  public:
@@ -176,7 +179,7 @@
   // |SetUp()| doesn't activate session if this is set to false.
   bool start_session_;
   MaterialDesignController::Mode material_mode_;
-  std::unique_ptr<AshTestEnvironment> ash_test_environment_;
+  std::unique_ptr<content::TestBrowserThreadBundle> thread_bundle_;
   std::unique_ptr<AshTestHelper> ash_test_helper_;
   std::unique_ptr<ui::test::EventGenerator> event_generator_;
 #if defined(OS_WIN)