Get rid of the HInstanceSize instruction.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index a51d67f3e090553b6c3c8dbd334f4b100a1043ac..7a48a44cee01e0472342c117dc1d6819df81a01a 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -126,7 +126,6 @@ class LChunkBuilder;
   V(InnerAllocatedObject)                      \
   V(InstanceOf)                                \
   V(InstanceOfKnownGlobal)                     \
-  V(InstanceSize)                              \
   V(InvokeFunction)                            \
   V(IsConstructCallAndBranch)                  \
   V(IsObjectAndBranch)                         \
@@ -4450,26 +4449,6 @@ class HInstanceOfKnownGlobal V8_FINAL : public HTemplateInstruction<2> {
 };
 
 
-// TODO(mstarzinger): This instruction should be modeled as a load of the map
-// field followed by a load of the instance size field once HLoadNamedField is
-// flexible enough to accommodate byte-field loads.
-class HInstanceSize V8_FINAL : public HTemplateInstruction<1> {
- public:
-  explicit HInstanceSize(HValue* object) {
-    SetOperandAt(0, object);
-    set_representation(Representation::Integer32());
-  }
-
-  HValue* object() { return OperandAt(0); }
-
-  virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
-    return Representation::Tagged();
-  }
-
-  DECLARE_CONCRETE_INSTRUCTION(InstanceSize)
-};
-
-
 class HPower V8_FINAL : public HTemplateInstruction<2> {
  public:
   static HInstruction* New(Zone* zone,
@@ -5805,6 +5784,12 @@ class HObjectAccess V8_FINAL {
     return HObjectAccess(kMaps, JSObject::kMapOffset);
   }
 
+  static HObjectAccess ForMapInstanceSize() {
+    return HObjectAccess(kInobject,
+                         Map::kInstanceSizeOffset,
+                         Representation::Byte());
+  }
+
   static HObjectAccess ForPropertyCellValue() {
     return HObjectAccess(kInobject, PropertyCell::kValueOffset);
   }