Reland: Fix bug in field type tracking and polymorphic inlining.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
===================================================================
--- runtime/vm/flow_graph.h	(revision 27690)
+++ runtime/vm/flow_graph.h	(working copy)
@@ -48,6 +48,10 @@
             GraphEntryInstr* graph_entry,
             intptr_t max_block_id);
 
+  const FlowGraphBuilder& builder() const {
+    return builder_;
+  }
+
   // Function properties.
   const ParsedFunction& parsed_function() const {
     return parsed_function_;
@@ -246,6 +250,7 @@
   intptr_t max_block_id_;
 
   // Flow graph fields.
+  const FlowGraphBuilder& builder_;
   const ParsedFunction& parsed_function_;
   const intptr_t num_copied_params_;
   const intptr_t num_non_copied_params_;