Change ppapi C++ comment style into C.

ppapi/c/ppb_core.h

Index: ppapi/c/ppb_core.h
diff --git a/ppapi/c/ppb_core.h b/ppapi/c/ppb_core.h
index b26e25f3b354f6df967bb8eac0f773550af9ba54..0d27937ff062f864b64b950abe7cc0ff1f687bba 100644
--- a/ppapi/c/ppb_core.h
+++ b/ppapi/c/ppb_core.h
@@ -1,7 +1,7 @@
-// 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_CORE_H_
 #define PPAPI_C_PPB_CORE_H_
 
@@ -90,4 +90,5 @@ struct PPB_Core {
  * @}
  * End addtogroup PPB
  */
-#endif  // PPAPI_C_DEV_PPB_CORE_DEV_H_
+#endif  /* PPAPI_C_DEV_PPB_CORE_DEV_H_ */
+