Simplify StringCharCodeAt in non-crankshaft codegen.

src/ia32/ic-ia32.cc

Index: src/ia32/ic-ia32.cc
diff --git a/src/ia32/ic-ia32.cc b/src/ia32/ic-ia32.cc
index 1168932057fb59aa36b3725be9017ee163f9672d..e93353e5dd660ee7d59474c62544fc17d9a24cb0 100644
--- a/src/ia32/ic-ia32.cc
+++ b/src/ia32/ic-ia32.cc
@@ -606,14 +606,12 @@ void KeyedLoadIC::GenerateString(MacroAssembler* masm) {
 
   Register receiver = edx;
   Register index = eax;
-  Register scratch1 = ebx;
-  Register scratch2 = ecx;
+  Register scratch = ecx;
   Register result = eax;
 
   StringCharAtGenerator char_at_generator(receiver,
                                           index,
-                                          scratch1,
-                                          scratch2,
+                                          scratch,
                                           result,
                                           &miss,  // When not a string.
                                           &miss,  // When not a number.