MacViews: Add native drop shadow to dialogs on OSX < 10.10.

ui/views/widget/native_widget_mac.mm

Index: ui/views/widget/native_widget_mac.mm
diff --git a/ui/views/widget/native_widget_mac.mm b/ui/views/widget/native_widget_mac.mm
index e34f61d29a401810224eab5a67c3bf6cf9689f99..3b848f43713cb0346d3845599044667c87ca8c25 100644
--- a/ui/views/widget/native_widget_mac.mm
+++ b/ui/views/widget/native_widget_mac.mm
@@ -502,9 +502,18 @@ void NativeWidgetMac::RunShellDrag(View* view,
 }
 
 void NativeWidgetMac::SchedulePaintInRect(const gfx::Rect& rect) {
-  // TODO(tapted): This should use setNeedsDisplayInRect:, once the coordinate
-  // system of |rect| has been converted.
-  [GetNativeView() setNeedsDisplay:YES];
+  // |rect| is relative to coordinate system of the window.
+  NSRect window_frame = [GetNativeWindow() frame];
+  // Convert rect to AppKit coordinate system.
+  NSRect target_rect_window =
+      NSMakeRect(rect.x(), window_frame.size.height - rect.y() - rect.height(),
+                 rect.width(), rect.height());
+  // Now target_rect is in the Appkit window's coordinate system. Convert it to
+  // native view's coordinate system.
+  NSView* native_view = GetNativeView();
+  NSRect target_rect_view =
+      [native_view convertRect:target_rect_window fromView:nil];
+  [native_view setNeedsDisplayInRect:target_rect_view];
   if (bridge_ && bridge_->layer())
     bridge_->layer()->SchedulePaint(rect);
 }