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

runtime/vm/growable_array.h

Index: runtime/vm/growable_array.h
diff --git a/runtime/vm/growable_array.h b/runtime/vm/growable_array.h
index ba6f80756bea9ba1b45b2423d0bfaf08cfaa413d..045c3e52cf2dd35bd1a0129c2284589ac17c1e39 100644
--- a/runtime/vm/growable_array.h
+++ b/runtime/vm/growable_array.h
@@ -161,10 +161,10 @@ class GrowableArray : public BaseGrowableArray<T, ValueObject> {
   explicit GrowableArray(intptr_t initial_capacity)
       : BaseGrowableArray<T, ValueObject>(
           initial_capacity,
-          ASSERT_NOTNULL(Isolate::Current()->current_zone())) {}
+          ASSERT_NOTNULL(Thread::Current()->zone())) {}
   GrowableArray()
       : BaseGrowableArray<T, ValueObject>(
-          ASSERT_NOTNULL(Isolate::Current()->current_zone())) {}
+          ASSERT_NOTNULL(Thread::Current()->zone())) {}
 };
 
 
@@ -177,10 +177,10 @@ class ZoneGrowableArray : public BaseGrowableArray<T, ZoneAllocated> {
   explicit ZoneGrowableArray(intptr_t initial_capacity)
       : BaseGrowableArray<T, ZoneAllocated>(
           initial_capacity,
-          ASSERT_NOTNULL(Isolate::Current()->current_zone())) {}
+          ASSERT_NOTNULL(Thread::Current()->zone())) {}
   ZoneGrowableArray()
       : BaseGrowableArray<T, ZoneAllocated>(
-          ASSERT_NOTNULL(Isolate::Current()->current_zone())) {}
+          ASSERT_NOTNULL(Thread::Current()->zone())) {}
 };