Runs most aura tests with both backends

ui/aura/test/aura_test_base.h

Index: ui/aura/test/aura_test_base.h
diff --git a/ui/aura/test/aura_test_base.h b/ui/aura/test/aura_test_base.h
index 84e72893beca95c876292e57c8cbd5a5ef392450..a76aa170ad55e28da77c0f53610d7652ad72309c 100644
--- a/ui/aura/test/aura_test_base.h
+++ b/ui/aura/test/aura_test_base.h
@@ -27,6 +27,8 @@ class WindowTreeClientDelegate;
 
 namespace test {
 
+enum class BackendType { CLASSIC, MUS };
+
 // A base class for aura unit tests.
 // TODO(beng): Instances of this test will create and own a RootWindow.
 class AuraTestBase : public testing::Test,
@@ -58,6 +60,10 @@ class AuraTestBase : public testing::Test,
   // Turns on mus. Must be called before SetUp().
   void EnableMus();
 
+  // Used to configure the backend. This is exposed to make parameterized tests
+  // easy to write. This *must* be called from SetUp().
+  void ConfigureBackend(BackendType type);
+
   void RunAllPendingInMessageLoop();
 
   void ParentWindow(Window* window);
@@ -128,6 +134,22 @@ class AuraTestBase : public testing::Test,
   DISALLOW_COPY_AND_ASSIGN(AuraTestBase);
 };
 
+// Use as a base class for tests that want to target both backends.
+class AuraTestBaseWithType : public AuraTestBase,
+                             public ::testing::WithParamInterface<BackendType> {
+ public:
+  AuraTestBaseWithType();
+  ~AuraTestBaseWithType() override;
+
+  // AuraTestBase:
+  void SetUp() override;
+
+ private:
+  bool setup_called_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(AuraTestBaseWithType);
+};
+
 }  // namespace test
 }  // namespace aura