Revert 186925 since it breaks many of the builds on the bots (e.g.

webkit/plugins/ppapi/host_var_tracker.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 "webkit/plugins/ppapi/host_var_tracker.h"
 
 #include "base/logging.h"
 #include "ppapi/c/pp_var.h"
 #include "webkit/plugins/ppapi/host_array_buffer_var.h"
 #include "webkit/plugins/ppapi/npobject_var.h"
 #include "webkit/plugins/ppapi/ppapi_plugin_instance.h"
 
 using ppapi::ArrayBufferVar;
 using ppapi::NPObjectVar;
 
 namespace webkit {
 namespace ppapi {
 
-HostVarTracker::HostVarTracker()
-  : VarTracker(SINGLE_THREADED) {
+HostVarTracker::HostVarTracker() {
 }
 
 HostVarTracker::~HostVarTracker() {
 }
 
 ArrayBufferVar* HostVarTracker::CreateArrayBuffer(uint32 size_in_bytes) {
   return new HostArrayBufferVar(size_in_bytes);
 }
 
 void HostVarTracker::AddNPObjectVar(NPObjectVar* object_var) {
-  CheckThreadingPreconditions();
+  DCHECK(CalledOnValidThread());
 
   InstanceMap::iterator found_instance = instance_map_.find(
       object_var->pp_instance());
   if (found_instance == instance_map_.end()) {
     // Lazily create the instance map.
     DCHECK(object_var->pp_instance() != 0);
     found_instance = instance_map_.insert(std::make_pair(
         object_var->pp_instance(),
         linked_ptr<NPObjectToNPObjectVarMap>(new NPObjectToNPObjectVarMap))).
             first;
   }
   NPObjectToNPObjectVarMap* np_object_map = found_instance->second.get();
 
   DCHECK(np_object_map->find(object_var->np_object()) ==
          np_object_map->end()) << "NPObjectVar already in map";
   np_object_map->insert(std::make_pair(object_var->np_object(), object_var));
 }
 
 void HostVarTracker::RemoveNPObjectVar(NPObjectVar* object_var) {
-  CheckThreadingPreconditions();
+  DCHECK(CalledOnValidThread());
 
   InstanceMap::iterator found_instance = instance_map_.find(
       object_var->pp_instance());
   if (found_instance == instance_map_.end()) {
     NOTREACHED() << "NPObjectVar has invalid instance.";
     return;
   }
   NPObjectToNPObjectVarMap* np_object_map = found_instance->second.get();
 
   NPObjectToNPObjectVarMap::iterator found_object =
       np_object_map->find(object_var->np_object());
   if (found_object == np_object_map->end()) {
     NOTREACHED() << "NPObjectVar not registered.";
     return;
   }
   if (found_object->second != object_var) {
     NOTREACHED() << "NPObjectVar doesn't match.";
     return;
   }
   np_object_map->erase(found_object);
 }
 
 NPObjectVar* HostVarTracker::NPObjectVarForNPObject(PP_Instance instance,
                                                     NPObject* np_object) {
-  CheckThreadingPreconditions();
+  DCHECK(CalledOnValidThread());
 
   InstanceMap::iterator found_instance = instance_map_.find(instance);
   if (found_instance == instance_map_.end())
     return NULL;  // No such instance.
   NPObjectToNPObjectVarMap* np_object_map = found_instance->second.get();
 
   NPObjectToNPObjectVarMap::iterator found_object =
       np_object_map->find(np_object);
   if (found_object == np_object_map->end())
     return NULL;  // No such object.
   return found_object->second;
 }
 
 int HostVarTracker::GetLiveNPObjectVarsForInstance(PP_Instance instance) const {
-  CheckThreadingPreconditions();
+  DCHECK(CalledOnValidThread());
 
   InstanceMap::const_iterator found = instance_map_.find(instance);
   if (found == instance_map_.end())
     return 0;
   return static_cast<int>(found->second->size());
 }
 
 void HostVarTracker::DidDeleteInstance(PP_Instance instance) {
-  CheckThreadingPreconditions();
+  DCHECK(CalledOnValidThread());
 
   InstanceMap::iterator found_instance = instance_map_.find(instance);
   if (found_instance == instance_map_.end())
     return;  // Nothing to do.
   NPObjectToNPObjectVarMap* np_object_map = found_instance->second.get();
 
   // Force delete all var references. ForceReleaseNPObject() will cause
   // this object, and potentially others it references, to be removed from
   // |np_object_map|.
   while (!np_object_map->empty()) {
@@ skipping 12 matching lines @@
     NOTREACHED();
     return;
   }
   iter->second.ref_count = 0;
   DCHECK(iter->second.track_with_no_reference_count == 0);
   DeleteObjectInfoIfNecessary(iter);
 }
 
 }  // namespace ppapi
 }  // namespace webkit