Add external strings support to regexp in generated code.

src/ia32/codegen-ia32.cc

Index: src/ia32/codegen-ia32.cc
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 58eead772b067f9c5f550b0b53b2d18ba9d90f92..6d991acc735c86dddb8b9b546d26641ef0e0419a 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -568,10 +568,10 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ j(zero, call_runtime);
   Register scratch = string;
   __ mov(scratch, FieldOperand(string, HeapObject::kMapOffset));
-  __ cmp(scratch, Immediate(factory->external_ascii_string_map()));
-  __ j(equal, &ascii_external, Label::kNear);
-  __ cmp(scratch, Immediate(factory->external_ascii_symbol_map()));
-  __ j(equal, &ascii_external, Label::kNear);
+  STATIC_ASSERT(kTwoByteStringTag == 0);
+  __ test_b(FieldOperand(scratch, Map::kInstanceTypeOffset),
+            kStringEncodingMask);
+  __ j(not_zero, &ascii_external);
   // Two-byte string.
   __ movzx_w(result, Operand(result, index, times_2, 0));
   __ jmp(&done);