Add HLoadRoot hydrogen instruction.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 059aa13322adb4dde769c9be9cf594fac8133cb4..7a7f9c94b1f7b9a2b48c199214c8a50d2da71ca5 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -3168,6 +3168,12 @@ void LCodeGen::DoLoadFunctionPrototype(LLoadFunctionPrototype* instr) {
 }
 
 
+void LCodeGen::DoLoadRoot(LLoadRoot* instr) {
+  Register result = ToRegister(instr->result());
+  __ LoadRoot(result, instr->index());
+}
+
+
 void LCodeGen::DoLoadExternalArrayPointer(
     LLoadExternalArrayPointer* instr) {
   Register to_reg = ToRegister(instr->result());