Gracefully handle multiple Flush/Reset/Decode with same id

ppapi/shared_impl/video_decoder_impl.cc

 // Copyright (c) 2011 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/video_decoder_impl.h"
 
 #include "base/logging.h"
 #include "gpu/command_buffer/client/gles2_implementation.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/proxy/plugin_resource_tracker.h"
@@ skipping 26 matching lines @@
   context3d_id_ = context3d_id;
   return true;
 }
 
 void VideoDecoderImpl::Destroy() {
   context3d_id_ = 0;
   gles2_impl_ = NULL;
   UnrefResource(context3d_id_);
 }
 
-void VideoDecoderImpl::SetFlushCallback(PP_CompletionCallback callback) {
+bool VideoDecoderImpl::SetFlushCallback(PP_CompletionCallback callback) {
   CHECK(callback.func);
-  DCHECK(!flush_callback_.func);
+  if (flush_callback_.func)
+    return false;
   flush_callback_ = callback;
+  return true;
 }
 
-void VideoDecoderImpl::SetResetCallback(PP_CompletionCallback callback) {
+bool VideoDecoderImpl::SetResetCallback(PP_CompletionCallback callback) {
   CHECK(callback.func);
-  DCHECK(!reset_callback_.func);
+  if (reset_callback_.func)
+    return false;
   reset_callback_ = callback;
+  return true;
 }
 
-void VideoDecoderImpl::SetBitstreamBufferCallback(
+bool VideoDecoderImpl::SetBitstreamBufferCallback(
     int32 bitstream_buffer_id, PP_CompletionCallback callback) {
-  CHECK(bitstream_buffer_callbacks_.insert(
-      std::make_pair(bitstream_buffer_id, callback)).second);
+  return bitstream_buffer_callbacks_.insert(
+      std::make_pair(bitstream_buffer_id, callback)).second;
 }
 
 void VideoDecoderImpl::RunFlushCallback(int32 result) {
   DCHECK(flush_callback_.func);
   PP_RunAndClearCompletionCallback(&flush_callback_, result);
 }
 
 void VideoDecoderImpl::RunResetCallback(int32 result) {
   DCHECK(reset_callback_.func);
   PP_RunAndClearCompletionCallback(&reset_callback_, result);
@@ skipping 23 matching lines @@
   const PP_VideoConfigElement* current = configs_to_copy;
   while (current && *current != PP_VIDEOATTR_DICTIONARY_TERMINATOR) {
     out_configs->push_back(*current);
     out_configs->push_back(*(current + 1));
     current += 2;
   }
   return true;
 }
 
 }  // namespace ppapi