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..8ee2a6d7de3021510f2d1474f400b85a11a01558 100644
--- a/ui/views/widget/native_widget_mac.mm
+++ b/ui/views/widget/native_widget_mac.mm
@@ -502,9 +502,15 @@ 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 client area of the window.

[tapted, 2016/02/10 02:28:02]

needs a rebase off the other CL (probably the order that they land doesn't
matter since it's a performance optimization)

[karandeepb, 2016/02/11 00:30:09]

Done.

+  NSWindow* window = GetNativeWindow();
+  NSRect client_rect = [window contentRectForFrameRect:[window frame]];
+  NSRect target_rect = rect.ToCGRect();
+
+  // Convert to Appkit coordinate system (origin at bottom left).
+  target_rect.origin.y =
+      NSHeight(client_rect) - target_rect.origin.y - NSHeight(target_rect);
+  [GetNativeView() setNeedsDisplayInRect:target_rect];
   if (bridge_ && bridge_->layer())
     bridge_->layer()->SchedulePaint(rect);
 }