Add CHECKs to ensure that PPAPI resources are created on the right thread

ppapi/shared_impl/resource_tracker.h

Index: ppapi/shared_impl/resource_tracker.h
diff --git a/ppapi/shared_impl/resource_tracker.h b/ppapi/shared_impl/resource_tracker.h
index 1c46bf5fe6f55f6141f1cf2905adc0006dfc4219..2f1c54e8b557603a06ac13b15e5588ac0a774b9e 100644
--- a/ppapi/shared_impl/resource_tracker.h
+++ b/ppapi/shared_impl/resource_tracker.h
@@ -11,6 +11,8 @@
 #include "base/hash_tables.h"
 #include "base/memory/linked_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
+#include "base/threading/thread_checker_impl.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/shared_impl/ppapi_shared_export.h"
@@ -63,11 +65,11 @@ class PPAPI_SHARED_EXPORT ResourceTracker {
   // the given resource. It's called from the resource destructor.
   virtual void RemoveResource(Resource* object);
 
+ private:
   // Calls LastPluginRefWasDeleted on the given resource object and cancels
   // pending callbacks for the resource.
   void LastPluginRefWasDeleted(Resource* object);
 
- private:
   typedef std::set<PP_Resource> ResourceSet;
 
   struct InstanceData {
@@ -96,6 +98,20 @@ class PPAPI_SHARED_EXPORT ResourceTracker {
 
   base::WeakPtrFactory<ResourceTracker> weak_ptr_factory_;
 
+  // TODO(raymes): We won't need to do thread checks once pepper calls are
+  // allowed off of the main thread.
+  // See http://code.google.com/p/chromium/issues/detail?id=92909.
+#ifdef ENABLE_PEPPER_THREADING
+  base::ThreadCheckerDoNothing thread_checker_;
+#else
+  // TODO(raymes): We've seen plugins (Flash) creating resources from random
+  // threads. Let's always crash for now in this case. Once we have a handle
+  // over how common this is, we can change ThreadCheckerImpl->ThreadChecker
+  // so that we only crash in debug mode. See
+  // https://code.google.com/p/chromium/issues/detail?id=146415.
+  base::ThreadCheckerImpl thread_checker_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(ResourceTracker);
 };