Fix bug in field type tracking and polymorphic inlining.

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
===================================================================
--- runtime/vm/flow_graph_builder.h	(revision 27611)
+++ runtime/vm/flow_graph_builder.h	(working copy)
@@ -105,6 +105,7 @@
   FlowGraphBuilder(ParsedFunction* parsed_function,
                    const Array& ic_data_array,
                    InlineExitCollector* exit_collector,
+                   GrowableArray<const Field*>* guarded_fields,
                    intptr_t osr_id);
 
   FlowGraph* BuildGraph();
@@ -147,6 +148,12 @@
   bool IsInlining() const { return (exit_collector_ != NULL); }
   InlineExitCollector* exit_collector() const { return exit_collector_; }
 
+  GrowableArray<const Field*>* guarded_fields() const {
+    return guarded_fields_;
+  }
+
+  void AddToGuardedFields(const Field& field) const;
+
   intptr_t args_pushed() const { return args_pushed_; }
   void add_args_pushed(intptr_t n) { args_pushed_ += n; }
 
@@ -169,6 +176,7 @@
   const intptr_t num_non_copied_params_;
   const intptr_t num_stack_locals_;  // Does not include any parameters.
   InlineExitCollector* const exit_collector_;
+  GrowableArray<const Field*>* guarded_fields_;
 
   intptr_t last_used_block_id_;
   intptr_t context_level_;