Switch FlushCallback to be a PP_CompletionCallback....

c/ppb_device_context_2d.h

 // Copyright (c) 2010 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 PPAPI_C_PPB_DEVICE_CONTEXT_2D_H_
 #define PPAPI_C_PPB_DEVICE_CONTEXT_2D_H_
 
 #include "ppapi/c/pp_module.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_stdint.h"
 
+typedef struct _pp_CompletionCallback PP_CompletionCallback;
 typedef struct _pp_Rect PP_Rect;
 
-// Callback function type for PaintImageData.
-typedef void (*PPB_DeviceContext2D_FlushCallback)(PP_Resource context,
-                                                  void* data);
-
 #define PPB_DEVICECONTEXT2D_INTERFACE "PPB_DeviceContext2D;1"
 
 typedef struct _ppb_DeviceContext2D {
   // The returned device context will not be bound to any plugin instance on
   // creation (call BindGraphicsDeviceContext on the plugin instance to do
   // that. The device context has a lifetime that can exceed that of the given
   // plugin instance.
   //
   // Set the is_always_opaque flag if you know that you will be painting only
   // opaque data to this device. This will disable blending when compositing
@@ skipping 128 matching lines @@
   //   there are internal references to the device that means it has not been
   //   internally destroyed (for example, if it is still bound to an instance)
   //   or due to other implementation details. As a result, you should be
   //   careful to check that flush callbacks are for the device you expect and
   //   that you're capable of handling callbacks for devices that you may have
   //   released your reference to.
   //
   // Shutdown: If a plugin instance is removed when a Flush is pending, the
   //   callback will not be executed.
   //
-  // Returns true on success or false on failure. Failure means the device
-  // context is invalid, you are requesting a synchronous flush from the main
-  // thread of the plugin, or you already have a Flush pending that has not
-  // issued its callback yet. In the failure case, nothing will be updated and
-  // no callback will be scheduled.
-  bool (*Flush)(PP_Resource device_context,
-                PPB_DeviceContext2D_FlushCallback callback,
-                void* callback_data);
+  // TODO(darin): We should ensure that the completion callback always runs, so
+  // that it is easier for consumers to manage memory referenced by a callback.
+  //
+  // Returns PP_OK on success, PP_Error_BadResource if the device context is
+  // invalid, PP_Error_BadArgument if the callback is null and Flush is being
+  // called from the main thread of the plugin, or PP_Error_InProgress if a
+  // Flush is already pending that has not issued its callback yet.  In the
+  // failure case, nothing will be updated and no callback will be scheduled.
+  int32_t (*Flush)(PP_Resource device_context, PP_CompletionCallback callback);
 
 } PPB_DeviceContext2D;
 
 #endif  // PPAPI_C_PPB_DEVICE_CONTEXT_2D_H_