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

ui/views/cocoa/bridged_native_widget.mm

Index: ui/views/cocoa/bridged_native_widget.mm
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index 6a4971bb827c5b17dad1302d43a29ca3bec829ea..e6d3276216f660a088780ca7438d35e772756ce1 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -682,6 +682,14 @@ void BridgedNativeWidget::OnSizeChanged() {
     if ([window_ inLiveResize])
       MaybeWaitForFrame(new_size);
   }
+
+  // 10.9 is unable to generate a window shadow from the composited CALayer, so
+  // use Quartz.
+  // We don't update the window mask during a live resize, instead it is done
+  // after the resize is completed in viewDidEndLiveResize: in
+  // BridgedContentView.
+  if (base::mac::IsOSMavericksOrEarlier() && ![window_ inLiveResize])
+    [bridged_view_ updateWindowMask];
 }
 
 void BridgedNativeWidget::OnVisibilityChanged() {
@@ -865,7 +873,14 @@ void BridgedNativeWidget::CreateLayer(ui::LayerType layer_type,
   // native shape is what's most appropriate for displaying sheets on Mac.
   if (translucent && !native_widget_mac_->IsWindowModalSheet()) {
     [window_ setOpaque:NO];
-    [window_ setBackgroundColor:[NSColor clearColor]];
+    // For Mac OS versions earlier than Yosemite, the Window server isn't able
+    // to generate a window shadow from the composited CALayer. To get around
+    // this, set an opaque background on the window and clip the window boundary
+    // in drawRect method of BridgedContentView. See crbug.com/543671.
+    if (base::mac::IsOSYosemiteOrLater())
+      [window_ setBackgroundColor:[NSColor clearColor]];
+    else
+      [window_ setBackgroundColor:[NSColor whiteColor]];

[tapted, 2016/02/11 01:47:23]

I just realised.. this `else` might not be needed. (i.e. can just use the
default window background?)

[karandeepb, 2016/02/11 04:16:04]

Done.

   }
 
   UpdateLayerProperties();