Add pointer cache field to external string for access in generated code.

test/mjsunit/string-externalize.js

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 21 matching lines @@
 function test() {
   var str = "";
 
   // Build an ascii cons string.
   for (var i = 0; i < size; i++) {
       str += String.fromCharCode(i & 0x7f);
   }
   assertTrue(isAsciiString(str));
 
   var twoByteExternalWithAsciiData =
-      "AA" + (function() { return "A"; })();
+      "AAAA" + (function() { return "A"; })();
   externalizeString(twoByteExternalWithAsciiData, true /* force two-byte */);
   assertFalse(isAsciiString(twoByteExternalWithAsciiData));
 
   var realTwoByteExternalString =
       "\u1234\u1234" + (function() { return "\u1234"; })();
   externalizeString(realTwoByteExternalString);
   assertFalse(isAsciiString(realTwoByteExternalString));
 
   assertTrue(isAsciiString(["a", twoByteExternalWithAsciiData].join("")));
 
@@ skipping 27 matching lines @@
   old_length = str2.length - realTwoByteExternalString.length;
   for (var i = 0; i < old_length; i++) {
     assertEquals(String.fromCharCode(i & 0x7f), str2[i]);
   }
   for (var i = old_length; i < str.length; i++) {
     assertEquals("\u1234", str2[i]);
   }
 
   // Flattened string should still be two-byte.
   assertFalse(isAsciiString(str2));
+
+  // Test buffered external strings.
+  var charat_str = new Array(5);
+  charat_str[0] = "0123456789ABCDEF0123456789ABCDEF\
+0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF\
+0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF\
+0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF\
+0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF";
+  charat_str[1] = "0123456789ABCDEF";
+  for (var i = 0; i < 6; i++) charat_str[1] += charat_str[1];
+  try {  // String can only be externalized once
+    externalizeString(charat_str[0], false);
+    externalizeString(charat_str[1], true);
+  } catch (ex) { }
+  charat_str[2] = charat_str[0].slice(0, -1);
+  charat_str[3] = charat_str[1].slice(0, -1);
+  charat_str[4] = charat_str[0] + charat_str[0];
+
+  for (var i = 0; i < 5; i++) {
+    assertEquals('B', charat_str[i].charAt(6*16 + 11));
+    assertEquals('C', charat_str[i].charAt(6*16 + 12));
+    assertEquals('A', charat_str[i].charAt(3*16 + 10));
+    assertEquals('B', charat_str[i].charAt(3*16 + 11));
+  }
 }
 
 // Run the test many times to ensure IC-s don't break things.
 for (var i = 0; i < 10; i++) {
   test();
 }
 
 // Clean up string to make Valgrind happy.
 gc();
 gc();