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

runtime/vm/hash_map.h

Index: runtime/vm/hash_map.h
diff --git a/runtime/vm/hash_map.h b/runtime/vm/hash_map.h
index 37fdc9bd3a320969d2ee580df00b41b788a5ee27..5c20d0442cd634601343c39ab8cae63c9837dc6a 100644
--- a/runtime/vm/hash_map.h
+++ b/runtime/vm/hash_map.h
@@ -106,9 +106,9 @@ DirectChainedHashMap<KeyValueTrait>::
     array_size_(other.array_size_),
     lists_size_(other.lists_size_),
     count_(other.count_),
-    array_(Isolate::Current()->current_zone()->
+    array_(Thread::Current()->zone()->
            Alloc<HashMapListElement>(other.array_size_)),
-    lists_(Isolate::Current()->current_zone()->
+    lists_(Thread::Current()->zone()->
            Alloc<HashMapListElement>(other.lists_size_)),
     free_list_head_(other.free_list_head_) {
   memmove(array_, other.array_, array_size_ * sizeof(HashMapListElement));
@@ -131,7 +131,7 @@ void DirectChainedHashMap<KeyValueTrait>::Resize(intptr_t new_size) {
   }
 
   HashMapListElement* new_array =
-      Isolate::Current()->current_zone()->Alloc<HashMapListElement>(new_size);
+      Thread::Current()->zone()->Alloc<HashMapListElement>(new_size);
   InitArray(new_array, new_size);
 
   HashMapListElement* old_array = array_;
@@ -169,7 +169,7 @@ void DirectChainedHashMap<T>::ResizeLists(intptr_t new_size) {
   ASSERT(new_size > lists_size_);
 
   HashMapListElement* new_lists =
-      Isolate::Current()->current_zone()->
+      Thread::Current()->zone()->
       Alloc<HashMapListElement>(new_size);
   InitArray(new_lists, new_size);