Reland "Removed default Isolate."

src/v8.cc

Index: src/v8.cc
diff --git a/src/v8.cc b/src/v8.cc
index 50d9184fc9bc579d08c74a87d9af54f1de85ffa7..c8d7e0381ed5c285fe092e853401ac1ae479a027 100644
--- a/src/v8.cc
+++ b/src/v8.cc
@@ -53,16 +53,6 @@ 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();