MacViews: Fix ViewTest.HandleAccelerator by faking window activation

ui/views/test/views_test_base.h

Index: ui/views/test/views_test_base.h
diff --git a/ui/views/test/views_test_base.h b/ui/views/test/views_test_base.h
index d3733b67fbbc495d9f38b3fb09dd39b743efa9db..ce2f2167d3cf479944515d84192509da085ff94c 100644
--- a/ui/views/test/views_test_base.h
+++ b/ui/views/test/views_test_base.h
@@ -34,6 +34,16 @@ class ViewsTestBase : public PlatformTest {
 
   void RunPendingMessages();
 
+  // When using desktop widgets on Mac, window activation is asynchronous
+  // because the window server is involved. A window may also be deactivated by
+  // a test running in parallel, making it flaky. Calling this method permits a
+  // unit test to "fake" this activation, causing it to be synchronous and
+  // per-process instead. Note that window activation on X11 is also
+  // asynchronous, and on Windows another process may "steal" activation from a
+  // parallelized unit_test run. However, a test can use non-desktop widgets
+  // there instead.
+  void EnableMacFakeWindowActivation();
+
   // Creates a widget of |type| with any platform specific data for use in
   // cross-platform tests.
   Widget::InitParams CreateParams(Widget::InitParams::Type type);