Revert "Removed default Isolate."

src/isolate.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ISOLATE_H_
 #define V8_ISOLATE_H_
 
 #include "../include/v8-debug.h"
 #include "allocation.h"
 #include "assert-scope.h"
@@ skipping 460 matching lines @@
   // True if at least one thread Enter'ed this isolate.
   bool IsInUse() { return entry_stack_ != NULL; }
 
   // Destroys the non-default isolates.
   // Sets default isolate into "has_been_disposed" state rather then destroying,
   // for legacy API reasons.
   void TearDown();
 
   static void GlobalTearDown();
 
+  bool IsDefaultIsolate() const { return this == default_isolate_; }
+
   static void SetCrashIfDefaultIsolateInitialized();
   // Ensures that process-wide resources and the default isolate have been
   // allocated. It is only necessary to call this method in rare cases, for
   // example if you are using V8 from within the body of a static initializer.
   // Safe to call multiple times.
   static void EnsureDefaultIsolate();
 
   // Find the PerThread for this particular (isolate, thread) combination
   // If one does not yet exist, return null.
   PerIsolateThreadData* FindPerThreadDataForThisThread();
@@ skipping 634 matching lines @@
 
     int entry_count;
     PerIsolateThreadData* previous_thread_data;
     Isolate* previous_isolate;
     EntryStackItem* previous_item;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(EntryStackItem);
   };
 
-  // This mutex protects highest_thread_id_ and thread_data_table_.
+  // This mutex protects highest_thread_id_, thread_data_table_ and
+  // default_isolate_.
   static Mutex process_wide_mutex_;
 
   static Thread::LocalStorageKey per_isolate_thread_data_key_;
   static Thread::LocalStorageKey isolate_key_;
   static Thread::LocalStorageKey thread_id_key_;
+  static Isolate* default_isolate_;
   static ThreadDataTable* thread_data_table_;
 
   // A global counter for all generated Isolates, might overflow.
   static Atomic32 isolate_counter_;
 
   void Deinit();
 
   static void SetIsolateThreadLocals(Isolate* isolate,
                                      PerIsolateThreadData* data);
 
@@ skipping 333 matching lines @@
   }
 
   EmbeddedVector<char, 128> filename_;
   FILE* file_;
   int scope_depth_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ISOLATE_H_