More x64 work.

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 0cb5cc7aed76559ac3a53754757a392ab25976bd..abffe50b190d0f813b3bcd618d25fb466d125675 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -146,6 +146,7 @@ class LCodeGen;
   V(StoreKeyedGeneric)                          \
   V(StoreNamedField)                            \
   V(StoreNamedGeneric)                          \
+  V(StringLength)                               \
   V(SubI)                                       \
   V(TaggedToI)                                  \
   V(Throw)                                      \
@@ -1550,6 +1551,19 @@ class LStoreKeyedGeneric: public LStoreKeyed {
 };
 
 
+class LStringLength: public LTemplateInstruction<1, 1, 0> {
+ public:
+  explicit LStringLength(LOperand* string) {
+    inputs_[0] = string;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringLength, "string-length")
+  DECLARE_HYDROGEN_ACCESSOR(StringLength)
+
+  LOperand* string() { return inputs_[0]; }
+};
+
+
 class LCheckFunction: public LTemplateInstruction<0, 1, 0> {
  public:
   explicit LCheckFunction(LOperand* value) {