Lazy implementation of final variables.

tests/language/final_syntax_test.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.
 
 main() {
   final f0 = 42;
   final f1; /// 01: compile-time error
   final int f2 = 87;
   final int f3; /// 02: compile-time error
   Expect.equals(42, f0);
   Expect.equals(87, f2);
 
   Expect.equals(42, F0); /// 03: compile-time error
   Expect.equals(87, F2); /// 04: compile-time error
 
   Expect.isTrue(P0 is Point);
-  Expect.isTrue(P1 is int);   /// 05: compile-time error
-  Expect.isTrue(P2 is Point); /// 06: compile-time error
-  Expect.isTrue(P3 is int);   /// 07: compile-time error
+  Expect.isTrue(P1 is int);
+  Expect.isTrue(P2 is Point);
+  Expect.isTrue(P3 is int);
 
   Expect.isTrue(A0 is int);
   Expect.isTrue(A1 is int);
-  Expect.isTrue(A2 is int); /// 08: compile-time error
+  Expect.isTrue(A2 is int); /// 08: runtime error
   Expect.isTrue(A3 is int); /// 08: continued
 
   Expect.isTrue(C0.X is C1);
   Expect.isTrue(C0.X.x is C1); /// 09: compile-time error
 
   Expect.equals("Hello 42", B2);
-  Expect.equals("42Hello", B3); /// 10: compile-time error
+  Expect.equals("42Hello", B3); /// 10: runtime error
 }
 
 final F0 = 42;
 final F1;                 /// 03: continued
 final int F2 = 87;
 final int F3;             /// 04: continued
 
 class Point {
   final x, y;
   const Point(this.x, this.y);
   operator +(int other) => x;
 }
 
 // Check that compile time expressions can include invocations of
 // user-defined const constructors.
 final P0 = const Point(0, 0);
-final P1 = const Point(0, 0) + 1; /// 05: continued
-final P2 = new Point(0, 0);       /// 06: continued
-final P3 = new Point(0, 0) + 1;   /// 07: continued
+final P1 = const Point(0, 0) + 1;
+final P2 = new Point(0, 0);
+final P3 = new Point(0, 0) + 1;
 
 // Check that we cannot have cyclic references in compile time
 // expressions.
 final A0 = 42;
 final A1 = A0 + 1;
 final A2 = A3 + 1; /// 08: continued
 final A3 = A2 + 1; /// 08: continued
 
 class C0 {
   static final X = const C1();
 }
 
 class C1 {
   const C1()
       : x = C0.X /// 09: continued
   ;
   final x = null;
 }
 
 // Check that sub-expressions of binary + are numeric.
 final B0 = 42;
 final B1 = "Hello";
 final B2 = "$B1 $B0";
 final B3 = B0 + B1; /// 10: continued