Migrate most uses of Isolate::current_zone to Thread::zone.

runtime/vm/profiler_service.cc

Index: runtime/vm/profiler_service.cc
diff --git a/runtime/vm/profiler_service.cc b/runtime/vm/profiler_service.cc
index 5e8940a5b9262497da510752ccf91136b9dba599..fac0bf4b25fa05d07b0226a5dfd8206f8a58f31a 100644
--- a/runtime/vm/profiler_service.cc
+++ b/runtime/vm/profiler_service.cc
@@ -252,7 +252,7 @@ void ProfileCode::SetName(const char* name) {
     name_ = NULL;
   }
   intptr_t len = strlen(name);
-  name_ = Isolate::Current()->current_zone()->Alloc<const char>(len + 1);
+  name_ = Thread::Current()->zone()->Alloc<const char>(len + 1);
   strncpy(const_cast<char*>(name_), name, len);
   const_cast<char*>(name_)[len] = '\0';
 }