Revert "Removed default Isolate."

src/v8.cc

Index: src/v8.cc
diff --git a/src/v8.cc b/src/v8.cc
index 9cca201972bdb9c1f1c6d6e51e42f290083c2dbe..f8156ecbd7123d0c5415f8b7e0e821228e37ac40 100644
--- a/src/v8.cc
+++ b/src/v8.cc
@@ -53,6 +53,16 @@ bool V8::Initialize(Deserializer* des) {
 
 
 void V8::TearDown() {
+  Isolate* isolate = Isolate::Current();
+  ASSERT(isolate->IsDefaultIsolate());
+  if (!isolate->IsInitialized()) return;
+
+  // The isolate has to be torn down before clearing the LOperand
+  // caches so that the optimizing compiler thread (if running)
+  // doesn't see an inconsistent view of the lithium instructions.
+  isolate->TearDown();
+  delete isolate;
+
   Bootstrapper::TearDownExtensions();
   ElementsAccessor::TearDown();
   LOperand::TearDownCaches();