Run Crankshaft on a separate thread.

src/handles-inl.h

Index: src/handles-inl.h
diff --git a/src/handles-inl.h b/src/handles-inl.h
index a5c81cec56f1d0056be0d1066683fc27432a4362..47ca378095b1c3e8ab87f85a120dee734902768c 100644
--- a/src/handles-inl.h
+++ b/src/handles-inl.h
@@ -33,6 +33,7 @@
 #include "apiutils.h"
 #include "handles.h"
 #include "isolate.h"
+#include "v8threads.h"
 
 namespace v8 {
 namespace internal {
@@ -69,6 +70,15 @@ inline T* Handle<T>::operator*() const {
 
 HandleScope::HandleScope() {
   Isolate* isolate = Isolate::Current();
+
+  if (FLAG_optimize_in_parallel &&
+      !isolate->thread_manager()->IsLockedByCurrentThread()) {
+    has_isolate_lock_ = true;
+    isolate->thread_manager()->Lock();
+  } else {
+    has_isolate_lock_ = false;
+  }
+
   v8::ImplementationUtilities::HandleScopeData* current =
       isolate->handle_scope_data();
   isolate_ = isolate;
@@ -82,6 +92,15 @@ HandleScope::HandleScope(Isolate* isolate) {
   ASSERT(isolate == Isolate::Current());
   v8::ImplementationUtilities::HandleScopeData* current =
       isolate->handle_scope_data();
+
+  if (FLAG_optimize_in_parallel &&
+      !isolate->thread_manager()->IsLockedByCurrentThread()) {
+    has_isolate_lock_ = true;
+    isolate->thread_manager()->Lock();
+  } else {
+    has_isolate_lock_ = false;
+  }
+
   isolate_ = isolate;
   prev_next_ = current->next;
   prev_limit_ = current->limit;
@@ -91,6 +110,9 @@ HandleScope::HandleScope(Isolate* isolate) {
 
 HandleScope::~HandleScope() {
   CloseScope();
+  if (has_isolate_lock_) {
+    isolate_->thread_manager()->Unlock();
+  }
 }
 
 void HandleScope::CloseScope() {