Improve array to string conversion.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 32dda278d8c546a31bcb859badaaed0d0bd14074..be3f9a4a6f46ae0ab3549bb7ba49ebdddeff9a19 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1646,6 +1646,16 @@ LInstruction* LChunkBuilder::DoDateField(HDateField* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
+  LOperand* string = UseRegister(instr->string());
+  LOperand* index = UseRegister(instr->index());
+  LOperand* value = UseRegister(instr->value());
+  LSeqStringSetChar* result =
+      new(zone()) LSeqStringSetChar(instr->is_one_byte(), string, index, value);
+  return DefineAsRegister(result);
+}
+
+
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
   LOperand* value = UseRegisterOrConstantAtStart(instr->index());
   LOperand* length = UseRegister(instr->length());