Collect type feedback for fields.

runtime/vm/flow_graph_type_propagator.h

Index: runtime/vm/flow_graph_type_propagator.h
diff --git a/runtime/vm/flow_graph_type_propagator.h b/runtime/vm/flow_graph_type_propagator.h
index f01dc5f2dd6af2a3e3dcdb9cddf85792749c8602..57ce140f1305ae5a1a78bc92c85b77951ff10c45 100644
--- a/runtime/vm/flow_graph_type_propagator.h
+++ b/runtime/vm/flow_graph_type_propagator.h
@@ -18,6 +18,9 @@ class FlowGraphTypePropagator : public FlowGraphVisitor {
 
  private:
   void PropagateRecursive(BlockEntryInstr* block);
+  void HandleBranchOnNull(BlockEntryInstr* block);
+
+  void RollbackTo(intptr_t rollback_point);
 
   void VisitValue(Value* value);
 
@@ -35,6 +38,8 @@ class FlowGraphTypePropagator : public FlowGraphVisitor {
   // Mark definition as having given class id in all dominated instructions.
   void SetCid(Definition* value, intptr_t cid);
 
+  void MarkNonNullable(Definition* value);
+
   void AddToWorklist(Definition* defn);
   Definition* RemoveLastFromWorklist();
 
@@ -44,6 +49,8 @@ class FlowGraphTypePropagator : public FlowGraphVisitor {
 
   FlowGraph* flow_graph_;
 
+  BitVector* visited_blocks_;
+
   // Mapping between SSA values and their current reaching types. Valid
   // only during dominator tree traversal.
   GrowableArray<CompileType*> types_;