Remove some Isolate::current_zone() calls, as it gets the zone from mutator thread not the current …

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 6655af303bb89fda05a02c6a3a3da60a6eca7891..d5f34e2a6392fac1489de466c3b443606b1f2b3e 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -1545,15 +1545,16 @@ void BackgroundCompiler::Stop(BackgroundCompiler* task) {
 }
 
 
-void BackgroundCompiler::EnsureInit(Isolate* isolate) {
+void BackgroundCompiler::EnsureInit(Thread* thread) {
   bool start_task = false;
+  Isolate* isolate = thread->isolate();
   {
     MutexLocker ml(isolate->mutex());
     if (isolate->background_compiler() == NULL) {
       BackgroundCompiler* task = new BackgroundCompiler(isolate);
       isolate->set_background_compiler(task);
       isolate->set_background_compilation_queue(GrowableObjectArray::Handle(
-          isolate->current_zone(), GrowableObjectArray::New()));
+          thread->zone(), GrowableObjectArray::New()));
       start_task = true;
     }
   }