Allow specifying base offset when constructing Keyed hydrogen instructions

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index 86121f62a333fed565d6ecd668af5cde83a7699d..e3db375973473a1ff3bb4b78ba8ea4c2c6c56f4f 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -1628,7 +1628,7 @@ class LLoadKeyed V8_FINAL : public LTemplateInstruction<1, 2, 0> {
   LOperand* elements() { return inputs_[0]; }
   LOperand* key() { return inputs_[1]; }
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
-  uint32_t additional_index() const { return hydrogen()->index_offset(); }
+  uint32_t base_offset() const { return hydrogen()->base_offset(); }
   ElementsKind elements_kind() const {
     return hydrogen()->elements_kind();
   }
@@ -2184,7 +2184,7 @@ class LStoreKeyed V8_FINAL : public LTemplateInstruction<0, 3, 0> {
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
   bool NeedsCanonicalization() { return hydrogen()->NeedsCanonicalization(); }
-  uint32_t additional_index() const { return hydrogen()->index_offset(); }
+  uint32_t base_offset() const { return hydrogen()->base_offset(); }
 };