Removed a bunch of GetExistingThreadLocal calls by threading the Isolate.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 57b8ca28a3ef4cc3c8c1d8d9fabe8ad4f2e8754d..ffc567b73a92aae20c5dba34fa59da0685322e90 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -789,9 +789,9 @@ class MaybeObject BASE_EMBEDDED {
   }
 
   template<typename T>
-  inline bool ToHandle(Handle<T>* obj) {
+    inline bool ToHandle(Handle<T>* obj, Isolate* isolate) {
     if (IsFailure()) return false;
-    *obj = handle(T::cast(reinterpret_cast<Object*>(this)));
+    *obj = handle(T::cast(reinterpret_cast<Object*>(this)), isolate);
     return true;
   }