Move global V8::UseCrankshaft() into the Isolate.

src/v8.h

Index: src/v8.h
diff --git a/src/v8.h b/src/v8.h
index 47893e8215e443a2f05d366001dc8a855b9476f6..aee4890aa066a9a949346d522b3106174fba9ae3 100644
--- a/src/v8.h
+++ b/src/v8.h
@@ -83,7 +83,6 @@ class V8 : public AllStatic {
   static bool Initialize(Deserializer* des);
   static void TearDown();
   static bool IsRunning() { return is_running_; }
-  static bool UseCrankshaft() { return use_crankshaft_; }
   // To be dead you have to have lived
   // TODO(isolates): move IsDead to Isolate.
   static bool IsDead() { return has_fatal_error_ || has_been_disposed_; }
@@ -141,8 +140,6 @@ class V8 : public AllStatic {
   // True if engine has been shut down
   // (reset if engine is restarted)
   static bool has_been_disposed_;
-  // True if we are using the crankshaft optimizing compiler.
-  static bool use_crankshaft_;
   // List of callbacks when a Call completes.
   static List<CallCompletedCallback>* call_completed_callbacks_;
   // Allocator for external array buffers.