Fix performance regression after adding inlining support for operators, [], and []=.

sdk/lib/_internal/compiler/implementation/ssa/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/nodes.dart	(revision 22723)
+++ sdk/lib/_internal/compiler/implementation/ssa/nodes.dart	(working copy)
@@ -1127,6 +1127,12 @@
   HInstruction get checkedInput => inputs[0];
   bool isJsStatement() => true;
   bool canThrow() => true;
+
+  HInstruction unwrap() {
+    var checked = checkedInput;
+    while (checked is HCheck) checked = checked.checkedInput;
+    return checked;
+  }
 }
 
 class HBailoutTarget extends HInstruction {