src: update uses of deprecated NewExternal

V8 String::NewExternal is deprecated in 4.9. Migrate string_bytes.cc to
the alternatives.

PR-URL: #5462
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>

Author: ofrobots

src/string_bytes.cc

@@ -77,7 +77,7 @@ class ExternString: public ResourceType {
       ExternString* h_str = new ExternString<ResourceType, TypeName>(isolate,
                                                                      data,
                                                                      length);
-      MaybeLocal<String> str = String::NewExternal(isolate, h_str);
+      MaybeLocal<String> str = NewExternal(isolate, h_str);
       isolate->AdjustAmountOfExternalAllocatedMemory(h_str->byte_length());
 
       if (str.IsEmpty()) {
@@ -93,6 +93,9 @@ class ExternString: public ResourceType {
   private:
     ExternString(Isolate* isolate, const TypeName* data, size_t length)
       : isolate_(isolate), data_(data), length_(length) { }
+    static MaybeLocal<String> NewExternal(Isolate* isolate,
+                                          ExternString* h_str);
+
     Isolate* isolate_;
     const TypeName* data_;
     size_t length_;
@@ -105,6 +108,20 @@ typedef ExternString<String::ExternalStringResource,
                      uint16_t> ExternTwoByteString;
 
 
+template <>
+MaybeLocal<String> ExternOneByteString::NewExternal(
+    Isolate* isolate, ExternOneByteString* h_str) {
+  return String::NewExternalOneByte(isolate, h_str);
+}
+
+
+template <>
+MaybeLocal<String> ExternTwoByteString::NewExternal(
+    Isolate* isolate, ExternTwoByteString* h_str) {
+  return String::NewExternalTwoByte(isolate, h_str);
+}
+
+
 //// Base 64 ////
 
 #define base64_encoded_size(size) ((size + 2 - ((size + 2) % 3)) / 3 * 4)