Add explicit smi-checks to smi comparisons.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
===================================================================
--- runtime/vm/flow_graph_optimizer.h	(revision 11616)
+++ runtime/vm/flow_graph_optimizer.h	(working copy)
@@ -32,6 +32,13 @@
   virtual void VisitBind(BindInstr* instr);
   virtual void VisitBranch(BranchInstr* instr);
 
+  // TODO(fschneider): Once we get rid of the distinction between Instruction
+  // and computation, this can be made private again.
+  BindInstr* InsertBefore(Instruction* instr,
+                          Computation* comp,
+                          Environment* env,
+                          BindInstr::UseKind use_kind);
+
  private:
   bool TryReplaceWithArrayOp(BindInstr* instr,
                              InstanceCallComp* comp,
@@ -51,11 +58,6 @@
 
   void AddCheckClass(BindInstr* instr, InstanceCallComp* comp, Value* value);
 
-  BindInstr* InsertBefore(Instruction* instr,
-                          Computation* comp,
-                          Environment* env,
-                          BindInstr::UseKind use_kind);
-
   BindInstr* InsertAfter(Instruction* instr,
                          Computation* comp,
                          Environment* env,