Add HLoadRoot hydrogen instruction.

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 8496deb081069cc3e2b4724281e6885069027c16..c68eecd0cbc1c166791d8c1d826b75ce69337319 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -120,6 +120,7 @@ class LCodeGen;
   V(LazyBailout)                                \
   V(LoadContextSlot)                            \
   V(LoadExternalArrayPointer)                   \
+  V(LoadRoot)                                   \
   V(LoadFieldByIndex)                           \
   V(LoadFunctionPrototype)                      \
   V(LoadGlobalCell)                             \
@@ -1535,6 +1536,15 @@ class LLoadFunctionPrototype V8_FINAL : public LTemplateInstruction<1, 1, 0> {
 };
 
 
+class LLoadRoot V8_FINAL : public LTemplateInstruction<1, 0, 0> {
+ public:
+  DECLARE_CONCRETE_INSTRUCTION(LoadRoot, "load-root")
+  DECLARE_HYDROGEN_ACCESSOR(LoadRoot)
+
+  Heap::RootListIndex index() const { return hydrogen()->index(); }
+};
+
+
 class LLoadExternalArrayPointer V8_FINAL
     : public LTemplateInstruction<1, 1, 0> {
  public: