Apply Kevin's suggestions, make branch-compare generation more robust

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
===================================================================
--- runtime/vm/flow_graph_builder.h	(revision 9777)
+++ runtime/vm/flow_graph_builder.h	(working copy)
@@ -315,8 +315,7 @@
       : ValueGraphVisitor(owner, temp_index),
         true_successor_address_(NULL),
         false_successor_address_(NULL),
-        condition_token_pos_(condition_token_pos) {
-  }
+        condition_token_pos_(condition_token_pos) { }
 
   TargetEntryInstr** true_successor_address() const {
     ASSERT(true_successor_address_ != NULL);
@@ -334,6 +333,13 @@
   // Closes the fragment and sets the output parameters.
   virtual void ReturnValue(Value* value);
 
+  // Either merges the computation into BranchInstr (Comparison, BooleanNegate)
+  // or adds a Bind instruction to the graph and returns its temporary value.
+  virtual void ReturnComputation(Computation* computation);
+
+  void MergeBranchWithComparison(ComparisonComp* comp);
+  void MergeBranchWithNegate(BooleanNegateComp* comp);
+
   // Output parameters.
   TargetEntryInstr** true_successor_address_;
   TargetEntryInstr** false_successor_address_;