Fix Unicode issues in dart2js and dart2dart.

sdk/lib/_internal/compiler/implementation/string_validator.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Check the validity of string literals.
 
 library stringvalidator;
 
 import "dart2jslib.dart";
 import "tree/tree.dart";
@@ skipping 78 matching lines @@
   DartString validateString(Token token,
                             int startOffset,
                             SourceString string,
                             StringQuoting quoting) {
     // We only need to check for invalid x and u escapes, for line
     // terminators in non-multiline strings, and for invalid Unicode
     // scalar values (either directly or as u-escape values).
     int length = 0;
     int index = startOffset;
     bool containsEscape = false;
+    bool previousWasLeadSurrogate = false;
+    bool invalidUtf16 = false;
     for(Iterator<int> iter = string.iterator(); iter.hasNext; length++) {
       index++;
       int code = iter.next();
       if (code == $BACKSLASH) {
         if (quoting.raw) continue;
         containsEscape = true;
         if (!iter.hasNext) {
           stringParseError("Incomplete escape sequence",token, index);
           return null;
         }
@@ skipping 52 matching lines @@
                 stringParseError("Invalid character in escape sequence",
                                  token, index);
                 return null;
               }
               value = value * 16 + hexDigitValue(code);
             }
           }
           code = value;
         }
       }
+      if (code >= 0x10000) length++;
+      assert(code <= 0x10ffff);
       // This handles both unescaped characters and the value of unicode
       // escapes.
-      if (!isUnicodeScalarValue(code)) {
-        stringParseError(
-            "Invalid Unicode scalar value U+${code.toRadixString(16)}",
-            token, index);
-        return null;
+      if (previousWasLeadSurrogate) {
+        if (!isUtf16TrailSurrogate(code)) {
+          invalidUtf16 = true;
+          break;
+        }
+        previousWasLeadSurrogate = false;
+      } else if (isUtf16LeadSurrogate(code)) {
+        previousWasLeadSurrogate = true;
+      } else if (!isUnicodeScalarValue(code)) {
+        invalidUtf16 = true;
+        break;
       }
     }
+    if (previousWasLeadSurrogate || invalidUtf16) {
+      stringParseError("Invalid Utf16 surrogate", token, index);
+      return null;
+    }
     // String literal successfully validated.
     if (quoting.raw || !containsEscape) {
       // A string without escapes could just as well have been raw.
       return new DartString.rawString(string, length);
     }
     return new DartString.escapedString(string, length);
   }
 }