Revert 187427 "PPAPI: Remove threading options; it's always on"

ppapi/shared_impl/resource_tracker.h

Index: ppapi/shared_impl/resource_tracker.h
===================================================================
--- ppapi/shared_impl/resource_tracker.h	(revision 187715)
+++ ppapi/shared_impl/resource_tracker.h	(working copy)
@@ -10,7 +10,6 @@
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
 #include "base/memory/linked_ptr.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "base/threading/thread_checker_impl.h"
@@ -24,12 +23,7 @@
 
 class PPAPI_SHARED_EXPORT ResourceTracker {
  public:
-  // A SINGLE_THREADED ResourceTracker will use a thread-checker to make sure
-  // it's always invoked on the same thread on which it was constructed. A
-  // THREAD_SAFE ResourceTracker will check that the ProxyLock is held. See
-  // CheckThreadingPreconditions() for more details.
-  enum ThreadMode { SINGLE_THREADED, THREAD_SAFE };
-  explicit ResourceTracker(ThreadMode thread_mode);
+  ResourceTracker();
   virtual ~ResourceTracker();
 
   // The returned pointer will be NULL if there is no resource. The reference
@@ -59,10 +53,6 @@
   // This calls AddResource and RemoveResource.
   friend class Resource;
 
-  // On the host-side, make sure we are called on the right thread. On the
-  // plugin side, make sure we have the proxy lock.
-  void CheckThreadingPreconditions() const;
-
   // Adds the given resource to the tracker, associating it with the instance
   // stored in the resource object. The new resource ID is returned, and the
   // resource will have 0 plugin refcount. This is called by the resource
@@ -108,11 +98,19 @@
 
   base::WeakPtrFactory<ResourceTracker> weak_ptr_factory_;
 
-  // On the host side, we want to check that we are only called on the main
-  // thread. This is to protect us from accidentally using the tracker from
-  // other threads (especially the IO thread). On the plugin side, the tracker
-  // is protected by the proxy lock and is thread-safe, so this will be NULL.
-  scoped_ptr<base::ThreadChecker> thread_checker_;
+  // 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);
 };