Tentative implementation of string slices (hidden under the flag --string-slices).

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index 9951d2540bb1cab9136db7c2acf028cc04584473..f178a559130f994c37d6a3267c5b9aeae28a68c3 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -2057,8 +2057,8 @@ LInstruction* LChunkBuilder::DoStringAdd(HStringAdd* instr) {
 
 
 LInstruction* LChunkBuilder::DoStringCharCodeAt(HStringCharCodeAt* instr) {
-  LOperand* string = UseRegister(instr->string());
-  LOperand* index = UseRegisterOrConstant(instr->index());
+  LOperand* string = UseTempRegister(instr->string());
+  LOperand* index = UseTempRegister(instr->index());
   LOperand* context = UseAny(instr->context());
   LStringCharCodeAt* result = new LStringCharCodeAt(context, string, index);
   return AssignEnvironment(AssignPointerMap(DefineAsRegister(result)));