Coverity: Fix several pass-by-values.

webkit/plugins/ppapi/ppb_video_capture_impl.h

Index: webkit/plugins/ppapi/ppb_video_capture_impl.h
diff --git a/webkit/plugins/ppapi/ppb_video_capture_impl.h b/webkit/plugins/ppapi/ppb_video_capture_impl.h
index bb5421bd7151c427994aa2c96c87ec751af7714b..9f61794d90890b8e4cb37ede92d1b14bca0460a4 100644
--- a/webkit/plugins/ppapi/ppb_video_capture_impl.h
+++ b/webkit/plugins/ppapi/ppb_video_capture_impl.h
@@ -53,12 +53,12 @@ class PPB_VideoCapture_Impl
   // PPB_VideoCapture_Shared implementation.
   virtual int32_t InternalEnumerateDevices(
       PP_Resource* devices,
-      PP_CompletionCallback callback) OVERRIDE;
+      const PP_CompletionCallback& callback) OVERRIDE;
   virtual int32_t InternalOpen(
       const std::string& device_id,
       const PP_VideoCaptureDeviceInfo_Dev& requested_info,
       uint32_t buffer_count,
-      PP_CompletionCallback callback) OVERRIDE;
+      const PP_CompletionCallback& callback) OVERRIDE;
   virtual int32_t InternalStartCapture() OVERRIDE;
   virtual int32_t InternalReuseBuffer(uint32_t buffer) OVERRIDE;
   virtual int32_t InternalStopCapture() OVERRIDE;