Recognize and optimize a.runtimeType == b.runtimeType pattern.

runtime/vm/precompiler.h

Index: runtime/vm/precompiler.h
diff --git a/runtime/vm/precompiler.h b/runtime/vm/precompiler.h
index 90b5f825b049e60ad3be74954faad7ed912b3af1..fa3530b3a228e6b8ffa2fad6da7ae5a0b3fd0eb0 100644
--- a/runtime/vm/precompiler.h
+++ b/runtime/vm/precompiler.h
@@ -356,10 +356,10 @@ class Precompiler : public ValueObject {
       Dart_QualifiedFunctionName embedder_entry_points[],
       bool reset_fields);
 
-  static RawError* CompileFunction(Thread* thread,
+  static RawError* CompileFunction(Precompiler* precompiler,
+                                   Thread* thread,
                                    Zone* zone,
-                                   const Function& function,
-                                   FieldTypeMap* field_type_map = NULL);
+                                   const Function& function);
 
   static RawObject* EvaluateStaticInitializer(const Field& field);
   static RawObject* ExecuteOnce(SequenceNode* fragment);
@@ -367,6 +367,15 @@ class Precompiler : public ValueObject {
   static RawFunction* CompileStaticInitializer(const Field& field,
                                                bool compute_type);
 
+  // Returns true if get:runtimeType is not overloaded by any class.
+  bool get_runtime_type_is_unique() const {
+    return get_runtime_type_is_unique_;
+  }
+
+  FieldTypeMap* field_type_map() {
+    return &field_type_map_;
+  }
+
  private:
   Precompiler(Thread* thread, bool reset_fields);
 
@@ -466,6 +475,8 @@ class Precompiler : public ValueObject {
   InstanceSet consts_to_retain_;
   FieldTypeMap field_type_map_;
   Error& error_;
+
+  bool get_runtime_type_is_unique_;
 };