Coverity: Fix several pass-by-values.

webkit/plugins/ppapi/ppb_video_capture_impl.cc

Index: webkit/plugins/ppapi/ppb_video_capture_impl.cc
diff --git a/webkit/plugins/ppapi/ppb_video_capture_impl.cc b/webkit/plugins/ppapi/ppb_video_capture_impl.cc
index cab216e8bcf8daff2f90c85adf7388424feacb25..c4879bd07f472107ffdcd5a8493a1ac1ace8ac69 100644
--- a/webkit/plugins/ppapi/ppb_video_capture_impl.cc
+++ b/webkit/plugins/ppapi/ppb_video_capture_impl.cc
@@ -173,7 +173,7 @@ void PPB_VideoCapture_Impl::OnInitialized(media::VideoCapture* capture,
 
 int32_t PPB_VideoCapture_Impl::InternalEnumerateDevices(
     PP_Resource* devices,
-    PP_CompletionCallback callback) {
+    const PP_CompletionCallback& callback) {
   PluginInstance* instance = ResourceHelper::GetPluginInstance(this);
   if (!instance)
     return PP_ERROR_FAILED;
@@ -191,7 +191,7 @@ int32_t PPB_VideoCapture_Impl::InternalOpen(
     const std::string& device_id,
     const PP_VideoCaptureDeviceInfo_Dev& requested_info,
     uint32_t buffer_count,
-    PP_CompletionCallback callback) {
+    const PP_CompletionCallback& callback) {
   // It is able to complete synchronously if the default device is used.
   bool sync_completion = device_id.empty();