Simplify generated code for trivial bailout methods.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
===================================================================
--- lib/compiler/implementation/ssa/nodes.dart	(revision 8532)
+++ lib/compiler/implementation/ssa/nodes.dart	(working copy)
@@ -984,6 +984,10 @@
   final int state;
   final HType guardedType;
   bool isOn = false;
+  // A list of sorted variable names to be able to share a common
+  // environment between type guards with the same [state].
+  List<String> sortedVariableNames;
+
   HTypeGuard(this.guardedType, this.state, List<HInstruction> env) : super(env);
 
   void prepareGvn() {
@@ -2490,6 +2494,10 @@
     return condition.start;
   }
 
+  HBasicBlock get loopHeader() {
+    return kind == DO_WHILE_LOOP ? body.start : condition.start;
+  }
+
   HBasicBlock get end() {
     if (updates !== null) return updates.end;
     if (kind == DO_WHILE_LOOP) {