Change ppapi C++ comment style into C.

ppapi/c/ppb_graphics_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.
-
+/* 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_GRAPHICS_2D_H_
 #define PPAPI_C_PPB_GRAPHICS_2D_H_
 
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_module.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_stdint.h"
 
 struct PP_CompletionCallback;
 struct PP_Point;
@@ skipping 188 matching lines @@
    *   callback will not be executed.
    * </dd>
    * </dl>
    *
    * Returns PP_OK on success, PP_Error_BadResource if the graphics 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.
    */
-  // 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.
+  /* 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.
+   */
   int32_t (*Flush)(PP_Resource graphics_2d,
                    struct PP_CompletionCallback callback);
 
 };
 
 /**
  * @}
  * End addtogroup PPB
  */
-#endif  // PPAPI_C_PPB_GRAPHICS_2D_H_
+#endif  /* PPAPI_C_PPB_GRAPHICS_2D_H_ */
+