Make cross-process CALayers work on Mac

ui/base/cocoa/remote_layer_api.h

+// 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.
+
+#ifndef UI_BASE_COCOA_REMOTE_LAYER_API_H_
+#define UI_BASE_COCOA_REMOTE_LAYER_API_H_
+
+#if defined(__OBJC__)
+#import <Cocoa/Cocoa.h>
+#endif  // __OBJC__
+
+#include "ui/base/ui_base_export.h"
+
+// The CGSConnectionID is used to create the CAContext in the process that is
+// going to share the CALayers that it is rendering to another process to
+// display.
+extern "C" {
+typedef uint32_t CGSConnectionID;
+CGSConnectionID CGSMainConnectionID(void);

[Ken Russell (switch to Gerrit), 2014/06/20 18:37:40]

Does it really work on systems which don't support this API (e.g. 10.8) to call
this API directly? I would think it would be necessary to look up this function
pointer dynamically.

[Avi (use Gerrit), 2014/06/20 18:42:18]

CGSMainConnectionID() has been around forever. You don't need to do a dynamic
lookup.

[ccameron, 2014/06/20 18:44:15]

Cause it's not documented, I'm not sure when it was introduced. I found a forum
posting (https://discussions.apple.com/message/8329852) where someone is
complaining in 2008 that something isn't working on 10.3 because it can't find
this symbol, so I suspect it has been around for a long time.

The try jobs didn't have any issues, and I think they're 10.6. Of note is that
the function won't actually get called unless the rest of the API is present
(which is only 10.9+).

+};
+
+// The CAContextID type identifies a CAContext across processes. This is the
+// token that is passed from the process that is sharing the CALayer that it is
+// rendering to the process that will be displaying that CALayer.
+typedef uint32_t CAContextID;
+
+#if defined(__OBJC__)
+
+// The CAContext has a static CAContextID which can be sent to another process.
+// When a CALayerHost is created using that CAContextID in another process, the
+// content displayed by that CALayerHost will be the content of the CALayer
+// that is set as the |layer| property on the CAContext.
+@interface CAContext : NSObject
++ (id)contextWithCGSConnection:(CAContextID)contextId
+                       options:(NSDictionary*)optionsDict;
+@property(readonly) CAContextID contextId;
+@property(retain) CALayer *layer;
+@end
+
+// The CALayerHost is created in the process that will display the content
+// being rendered by another process. Setting the |contextId| property on
+// an object of this class will make this layer display the content of the
+// CALayer that is set to the CAContext with that CAContextID in the layer
+// sharing process.
+@interface CALayerHost : CALayer
+@property CAContextID contextId;
+@end
+
+#endif // __OBJC__
+
+namespace ui {
+
+// This function will check if all of the interfaces listed above are supported
+// on the system, and return true if they are.
+bool UI_BASE_EXPORT RemoteLayerAPISupported();
+
+}  // namespace ui
+
+#endif  // UI_BASE_COCOA_REMOTE_LAYER_API_H_