MacViews: Fix failing mouse capture unittests.

ui/views/test/event_generator_delegate_mac.mm

Index: ui/views/test/event_generator_delegate_mac.mm
diff --git a/ui/views/test/event_generator_delegate_mac.mm b/ui/views/test/event_generator_delegate_mac.mm
index a1ab5cb466b875c339e567b8e9b1ace56adc840d..55005ea2c4647103ab53c465a2105e3f0cd20934 100644
--- a/ui/views/test/event_generator_delegate_mac.mm
+++ b/ui/views/test/event_generator_delegate_mac.mm
@@ -428,7 +428,9 @@ gfx::Point EventGeneratorDelegateMac::CenterOfTarget(
 gfx::Point EventGeneratorDelegateMac::CenterOfWindow(
     gfx::NativeWindow window) const {
   DCHECK_EQ(window, window_);
-  return gfx::ScreenRectFromNSRect([window frame]).CenterPoint();
+  // Assume the window is at the top-left of the coordinate system (even if
+  // AppKit has moved it into the work area) see ConvertRootPointToTarget().
+  return gfx::Point(NSWidth([window frame]) / 2, NSHeight([window frame]) / 2);
 }
 
 // Return the current owner of the EventGeneratorDelegate. May be null.