Pass isolate to BitVector constructor.

runtime/vm/flow_graph_allocator.cc

Index: runtime/vm/flow_graph_allocator.cc
===================================================================
--- runtime/vm/flow_graph_allocator.cc	(revision 40526)
+++ runtime/vm/flow_graph_allocator.cc	(working copy)
@@ -518,6 +518,7 @@
   const intptr_t block_count = postorder_.length();
   ASSERT(postorder_.Last()->IsGraphEntry());
   BitVector* current_interference_set = NULL;
+  Isolate* isolate = flow_graph_.isolate();
   for (intptr_t i = 0; i < (block_count - 1); i++) {
     BlockEntryInstr* block = postorder_[i];
 
@@ -535,8 +536,8 @@
 
     BlockInfo* loop_header = block_info->loop_header();
     if ((loop_header != NULL) && (loop_header->last_block() == block)) {
-      current_interference_set =
-          new BitVector(flow_graph_.max_virtual_register_number());
+      current_interference_set = new(isolate) BitVector(
+          isolate, flow_graph_.max_virtual_register_number());
       ASSERT(loop_header->backedge_interference() == NULL);
       // All values flowing into the loop header are live at the back-edge and
       // can interfere with phi moves.
@@ -2005,8 +2006,9 @@
 void ReachingDefs::AddPhi(PhiInstr* phi) {
   // TODO(johnmccutchan): Fix handling of PhiInstr with PairLocation.
   if (phi->reaching_defs() == NULL) {
-    phi->set_reaching_defs(
-        new BitVector(flow_graph_.max_virtual_register_number()));
+    Isolate* isolate = Isolate::Current();
+    phi->set_reaching_defs(new(isolate) BitVector(
+        isolate, flow_graph_.max_virtual_register_number()));
 
     // Compute initial set reaching defs set.
     bool depends_on_phi = false;