Add some support for the code-point code-unit distinction.

sdk/lib/_internal/compiler/implementation/scanner/token.dart

Index: sdk/lib/_internal/compiler/implementation/scanner/token.dart
diff --git a/sdk/lib/_internal/compiler/implementation/scanner/token.dart b/sdk/lib/_internal/compiler/implementation/scanner/token.dart
index a768b5038458be91960883793ce175f69e29d55d..4ef81cd0c7e066c369814d4953e3fd6fe7f46f99 100644
--- a/sdk/lib/_internal/compiler/implementation/scanner/token.dart
+++ b/sdk/lib/_internal/compiler/implementation/scanner/token.dart
@@ -231,6 +231,9 @@ class StringWrapper implements SourceString {
   bool isPrivate() => !isEmpty && identical(stringValue.charCodeAt(0), $_);
 }
 
+
+// TODO(erikcorry): Use the new code point iterator on String when it is
+// available.
 class StringCodeIterator implements Iterator<int> {
   final String string;
   int index;
@@ -246,7 +249,12 @@ class StringCodeIterator implements Iterator<int> {
   }
 
   bool get hasNext => index < end;
-  int next() => string.charCodeAt(index++);
+  int next() {
+    int charCode = string.charCodeAt(index++);
+    // Skip trail surrogate.
+    if (charCode >= String.SMP_CODE_POINT_BASE) index++;
+    return charCode;
+  }
 }
 
 class BeginGroupToken extends StringToken {