Support sync mojo IPCs to and from bindings running on a sequence.

mojo/public/cpp/bindings/sync_handle_registry.h

Index: mojo/public/cpp/bindings/sync_handle_registry.h
diff --git a/mojo/public/cpp/bindings/sync_handle_registry.h b/mojo/public/cpp/bindings/sync_handle_registry.h
index b5415af80dfb64fa20b453b14262e1cc40264a7f..881082ece30a04f31e71cf3a7a38bee7ebc82c4b 100644
--- a/mojo/public/cpp/bindings/sync_handle_registry.h
+++ b/mojo/public/cpp/bindings/sync_handle_registry.h
@@ -10,20 +10,20 @@
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/threading/thread_checker.h"
+#include "base/sequence_checker.h"
 #include "mojo/public/cpp/bindings/bindings_export.h"
 #include "mojo/public/cpp/system/core.h"
 
 namespace mojo {
 
-// SyncHandleRegistry is a thread-local storage to register handles that want to
-// be watched together.
+// SyncHandleRegistry is a sequence-local storage to register handles that want
+// to be watched together.
 //
 // This class is not thread safe.
 class MOJO_CPP_BINDINGS_EXPORT SyncHandleRegistry
-    : public base::RefCounted<SyncHandleRegistry> {
+    : public base::RefCountedThreadSafe<SyncHandleRegistry> {
  public:
-  // Returns a thread-local object.
+  // Returns a sequence-local object.
   static scoped_refptr<SyncHandleRegistry> current();
 
   using HandleCallback = base::Callback<void(MojoResult)>;
@@ -41,7 +41,7 @@ class MOJO_CPP_BINDINGS_EXPORT SyncHandleRegistry
   bool WatchAllHandles(const bool* should_stop[], size_t count);
 
  private:
-  friend class base::RefCounted<SyncHandleRegistry>;
+  friend class base::RefCountedThreadSafe<SyncHandleRegistry>;
 
   struct HandleHasher {
     size_t operator()(const Handle& handle) const {
@@ -57,7 +57,7 @@ class MOJO_CPP_BINDINGS_EXPORT SyncHandleRegistry
 
   ScopedHandle wait_set_handle_;
 
-  base::ThreadChecker thread_checker_;
+  base::SequenceChecker sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncHandleRegistry);
 };