Porting r10023 and r10054 to x64 (pointer cache for external strings).

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h
index a0648cec6433bb8acc17789d74f33fdc86e1bfaf..2e807510333a27af48b55e979e209d5d449bc6b9 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -69,6 +69,21 @@ class CodeGenerator: public AstVisitor {
 };
 
 
+class StringCharLoadGenerator : public AllStatic {
+ public:
+  // Generates the code for handling different string types and loading the
+  // indexed character into |result|.  We expect |index| as untagged input and
+  // |result| as untagged output.
+  static void Generate(MacroAssembler* masm,
+                       Register string,
+                       Register index,
+                       Register result,
+                       Label* call_runtime);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(StringCharLoadGenerator);
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODEGEN_X64_H_