Coverity: Fix several pass-by-values.

ppapi/shared_impl/ppb_video_capture_shared.cc

 // Copyright (c) 2012 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.
 
 #include "ppapi/shared_impl/ppb_video_capture_shared.h"
 
 #include "base/logging.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/shared_impl/ppb_device_ref_shared.h"
 #include "ppapi/shared_impl/ppb_resource_array_shared.h"
@@ skipping 19 matching lines @@
 
 PPB_VideoCapture_Shared::~PPB_VideoCapture_Shared() {
 }
 
 thunk::PPB_VideoCapture_API* PPB_VideoCapture_Shared::AsPPB_VideoCapture_API() {
   return this;
 }
 
 int32_t PPB_VideoCapture_Shared::EnumerateDevices(
     PP_Resource* devices,
-    PP_CompletionCallback callback) {
+    const PP_CompletionCallback& callback) {
   if (!callback.func)
     return PP_ERROR_BLOCKS_MAIN_THREAD;
   if (TrackedCallback::IsPending(enumerate_devices_callback_))
     return PP_ERROR_INPROGRESS;
 
   return InternalEnumerateDevices(devices, callback);
 }
 
 int32_t PPB_VideoCapture_Shared::Open(
     const std::string& device_id,
     const PP_VideoCaptureDeviceInfo_Dev& requested_info,
     uint32_t buffer_count,
-    PP_CompletionCallback callback) {
+    const PP_CompletionCallback& callback) {
   if (open_state_ != BEFORE_OPEN)
     return PP_ERROR_FAILED;
 
   if (TrackedCallback::IsPending(open_callback_))
     return PP_ERROR_INPROGRESS;
 
   return InternalOpen(device_id, requested_info, buffer_count, callback);
 }
 
 int32_t PPB_VideoCapture_Shared::StartCapture() {
@@ skipping 116 matching lines @@
         }
         break;
     }
   }
 
   status_ = status;
   return true;
 }
 
 }  // namespace ppapi