Move WidgetActivationWaiter to a common place

ui/views/test/widget_test.h

Index: ui/views/test/widget_test.h
diff --git a/ui/views/test/widget_test.h b/ui/views/test/widget_test.h
index fe04891ec8648d1d735c5df4fd84a656257d21b3..5b02be7805dc395d01d73f464c26e7902963a0b4 100644
--- a/ui/views/test/widget_test.h
+++ b/ui/views/test/widget_test.h
@@ -6,10 +6,12 @@
 #define UI_VIEWS_TEST_WIDGET_TEST_H_
 
 #include "base/macros.h"
+#include "base/run_loop.h"
 #include "build/build_config.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/test/views_test_base.h"
 #include "ui/views/widget/widget_delegate.h"
+#include "ui/views/widget/widget_observer.h"
 
 namespace ui {
 namespace internal {
@@ -153,6 +155,25 @@ class TestInitialFocusWidgetDelegate : public TestDesktopWidgetDelegate {
   DISALLOW_COPY_AND_ASSIGN(TestInitialFocusWidgetDelegate);
 };
 
+// Spins a run loop until a Widget's activation reaches the desired state.
+class WidgetActivationWaiter : public WidgetObserver {
+ public:
+  WidgetActivationWaiter(Widget* widget, bool active);
+  ~WidgetActivationWaiter() override;
+
+  void Wait();

[sky, 2016/10/12 16:05:43]

Document what this does.

[Qiang(Joe) Xu, 2016/10/12 16:55:58]

Done.

+
+ private:
+  // views::WidgetObserver override:
+  void OnWidgetActivationChanged(Widget* widget, bool active) override;
+
+  base::RunLoop run_loop_;
+  bool observed_;
+  bool active_;
+
+  DISALLOW_COPY_AND_ASSIGN(WidgetActivationWaiter);
+};
+
 }  // namespace test
 }  // namespace views