Improve array to string conversion.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 9217a9407fc942e2ea077bec5cee802b8737299b..549de35e111caa47c98abf21bb1b615b32417694 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1437,6 +1437,15 @@ void LCodeGen::DoDateField(LDateField* instr) {
 }
 
 
+void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
+  Register string = ToRegister(instr->string());
+  Register index = ToRegister(instr->index());
+  Register value = ToRegister(instr->value());
+  SeqStringSetCharGenerator::Generate(
+      masm(), instr->is_one_byte(), string, index, value);
+}
+
+
 void LCodeGen::DoBitNotI(LBitNotI* instr) {
   LOperand* input = instr->value();
   ASSERT(input->Equals(instr->result()));