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

ui/views/cocoa/bridged_native_widget.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ui/views/cocoa/bridged_native_widget.h"
 
 #import <objc/runtime.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 832 matching lines @@
   layer()->SetFillsBoundsOpaquely(!translucent);
 
   // Use the regular window background for window modal sheets. The layer() will
   // still paint over most of it, but the native -[NSApp beginSheet:] animation
   // blocks the UI thread, so there's no way to invalidate the shadow to match
   // the composited layer. This assumes the native window shape is a good match
   // for the composited NonClientFrameView, which should be the case since the
   // 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 OSs earlier than Yosemite, we set an opaque background so that window
+    // server can generate a a drop shadow and border for dialogs. See
+    // crbug.com/543671.
+    if (base::mac::IsOSYosemiteOrLater())
+      [window_ setBackgroundColor:[NSColor clearColor]];
+    else
+      [window_ setBackgroundColor:[NSColor whiteColor]];
   }
 
   UpdateLayerProperties();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // BridgedNativeWidget, internal::InputMethodDelegate:
 
 ui::EventDispatchDetails BridgedNativeWidget::DispatchKeyEventPostIME(
     ui::KeyEvent* key) {
@@ skipping 347 matching lines @@
   [bridged_view_ setMouseDownCanMoveWindow:draggable];
   // AppKit will not update its cache of mouseDownCanMoveWindow unless something
   // changes. Previously we tried adding an NSView and removing it, but for some
   // reason it required reposting the mouse-down event, and didn't always work.
   // Calling the below seems to be an effective solution.
   [window_ setMovableByWindowBackground:NO];
   [window_ setMovableByWindowBackground:YES];
 }
 
 }  // namespace views