PPAPI: Remove threading options; it's always on

webkit/plugins/ppapi/host_var_tracker.cc

Index: webkit/plugins/ppapi/host_var_tracker.cc
diff --git a/webkit/plugins/ppapi/host_var_tracker.cc b/webkit/plugins/ppapi/host_var_tracker.cc
index 5d5349949a65c25be40fe195fca7a930b85e53a1..99518fde696a04be37bbfd2d4681244cf49bc836 100644
--- a/webkit/plugins/ppapi/host_var_tracker.cc
+++ b/webkit/plugins/ppapi/host_var_tracker.cc
@@ -16,7 +16,9 @@ using ppapi::NPObjectVar;
 namespace webkit {
 namespace ppapi {
 
-HostVarTracker::HostVarTracker() : last_shared_memory_map_id_(0) {
+HostVarTracker::HostVarTracker()
+  : VarTracker(SINGLE_THREADED),
+    last_shared_memory_map_id_(0) {
 }
 
 HostVarTracker::~HostVarTracker() {
@@ -33,7 +35,7 @@ ArrayBufferVar* HostVarTracker::CreateShmArrayBuffer(
 }
 
 void HostVarTracker::AddNPObjectVar(NPObjectVar* object_var) {
-  DCHECK(CalledOnValidThread());
+  CheckThreadingPreconditions();
 
   InstanceMap::iterator found_instance = instance_map_.find(
       object_var->pp_instance());
@@ -53,7 +55,7 @@ void HostVarTracker::AddNPObjectVar(NPObjectVar* object_var) {
 }
 
 void HostVarTracker::RemoveNPObjectVar(NPObjectVar* object_var) {
-  DCHECK(CalledOnValidThread());
+  CheckThreadingPreconditions();
 
   InstanceMap::iterator found_instance = instance_map_.find(
       object_var->pp_instance());
@@ -78,7 +80,7 @@ void HostVarTracker::RemoveNPObjectVar(NPObjectVar* object_var) {
 
 NPObjectVar* HostVarTracker::NPObjectVarForNPObject(PP_Instance instance,
                                                     NPObject* np_object) {
-  DCHECK(CalledOnValidThread());
+  CheckThreadingPreconditions();
 
   InstanceMap::iterator found_instance = instance_map_.find(instance);
   if (found_instance == instance_map_.end())
@@ -93,7 +95,7 @@ NPObjectVar* HostVarTracker::NPObjectVarForNPObject(PP_Instance instance,
 }
 
 int HostVarTracker::GetLiveNPObjectVarsForInstance(PP_Instance instance) const {
-  DCHECK(CalledOnValidThread());
+  CheckThreadingPreconditions();
 
   InstanceMap::const_iterator found = instance_map_.find(instance);
   if (found == instance_map_.end())
@@ -102,7 +104,7 @@ int HostVarTracker::GetLiveNPObjectVarsForInstance(PP_Instance instance) const {
 }
 
 void HostVarTracker::DidDeleteInstance(PP_Instance instance) {
-  DCHECK(CalledOnValidThread());
+  CheckThreadingPreconditions();
 
   InstanceMap::iterator found_instance = instance_map_.find(instance);
   if (found_instance == instance_map_.end())