Revert r8592: failures on checked mode and some web tests.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
===================================================================
--- lib/compiler/implementation/ssa/nodes.dart	(revision 8593)
+++ lib/compiler/implementation/ssa/nodes.dart	(working copy)
@@ -985,8 +985,6 @@
   final int state;
   final HType guardedType;
   bool isOn = false;
-  int checkedInputIndex = 0;
-
   HTypeGuard(this.guardedType, this.state, List<HInstruction> env) : super(env);
 
   void prepareGvn() {
@@ -994,7 +992,7 @@
     setUseGvn();
   }
 
-  HInstruction get guarded() => inputs[checkedInputIndex];
+  HInstruction get guarded() => inputs.last();
   HInstruction get checkedInput() => guarded;
 
   HType computeTypeFromInputTypes() {
@@ -1008,9 +1006,7 @@
   accept(HVisitor visitor) => visitor.visitTypeGuard(this);
   int typeCode() => 1;
   bool typeEquals(other) => other is HTypeGuard;
-  bool dataEquals(HTypeGuard other) {
-    return guarded == other.guarded && guardedType == other.guardedType;
-  }
+  bool dataEquals(HTypeGuard other) => guardedType == other.guardedType;
 }
 
 class HBoundsCheck extends HCheck {
@@ -2495,10 +2491,6 @@
     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) {