MacViews: Clip contents for non-rectangular windows.

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 6f5dec0f96864ede56c8a7cf940de5ebf964aa92..e3df3e51ff19bb5b716f002f3a91ce2a0f16ca4a 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -4,6 +4,7 @@
 
 #import "ui/views/cocoa/bridged_native_widget.h"
 
+#import <Quartz/Quartz.h>
 #import <objc/runtime.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -13,6 +14,7 @@
 #include "base/mac/mac_util.h"
 #import "base/mac/sdk_forward_declarations.h"
 #include "base/thread_task_runner_handle.h"
+#import "third_party/google_toolbox_for_mac/src/AppKit/GTMNSBezierPath+CGPath.h"
 #include "ui/accelerated_widget_mac/window_resize_helper_mac.h"
 #import "ui/base/cocoa/constrained_window/constrained_window_animation.h"
 #include "ui/base/hit_test.h"
@@ -683,13 +685,7 @@ void BridgedNativeWidget::OnSizeChanged() {
       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];
+  UpdateMaskPath();
 }
 
 void BridgedNativeWidget::OnVisibilityChanged() {
@@ -1244,4 +1240,33 @@ void BridgedNativeWidget::SetDraggable(bool draggable) {
   [window_ setMovableByWindowBackground:YES];
 }
 
+// TODO(karandeepb): Add tests to verify mask layer is correctly set up.

[tapted, 2016/03/04 04:15:01]

we don't usually have TODO: add tests in code comments :). You can make a bug
and assign it to yourself, but if it's not urgent we can usually just write the
tests and land them with the CL.

+void BridgedNativeWidget::UpdateMaskPath() {
+  [bridged_view_ updateWindowMask];
+
+  // We only set the mask layer for windows with non-rectangular masks.
+  if (![bridged_view_ windowMask]) {
+    // Removing a mask after adding one isn't currently supported.
+    DCHECK(![[compositor_superview_ layer] mask]);
+    return;
+  }
+
+  CAShapeLayer* mask_layer = base::mac::ObjCCastStrict<CAShapeLayer>(
+      [[compositor_superview_ layer] mask]);
+  if (mask_layer) {
+    [mask_layer setPath:[[bridged_view_ windowMask] gtm_CGPath]];
+    return;
+  }
+
+  // If mask layer does not exist yet, create one and set it as the background
+  // layer's mask. Clipping will be done based on the alpha channel of the mask
+  // layer.
+  mask_layer = [CAShapeLayer layer];
+  [mask_layer setPath:[[bridged_view_ windowMask] gtm_CGPath]];
+
+  CALayer* background_layer = [compositor_superview_ layer];
+  [background_layer setMask:mask_layer];
+  [background_layer setMasksToBounds:YES];
+}
+
 }  // namespace views