Update mock SDK 'double'.

pkg/analyzer/test/src/task/strong/checker_test.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 /// General type checking tests
 library analyzer.test.src.task.strong.checker_test;
 
 import 'package:unittest/unittest.dart';
@@ skipping 2033 matching lines @@
         /*severe:INVALID_METHOD_OVERRIDE*/ToVoid<dynamic> get g => null;
       }
        ''');
   });
 
   test('setter override, fuzzy arrows', () {
     checkFile('''
       typedef void ToVoid<T>(T x);
       class F {
         void set f(ToVoid<dynamic> x) {}
-        void set g(ToVoid<int> x) {} 
+        void set g(ToVoid<int> x) {}
         void set h(dynamic x) {}
         void set i(int x) {}
      }
 
       class G extends F {
         /*severe:INVALID_METHOD_OVERRIDE*/void set f(ToVoid<int> x) {}
         void set g(ToVoid<dynamic> x) {}
         void set h(int x) {}
         /*severe:INVALID_METHOD_OVERRIDE*/void set i(dynamic x) {}
       }
@@ skipping 271 matching lines @@
             double y = 0.0;
             y += 5;
             y += 3.14;
 
             num z = 0;
             z += 5;
             z += 3.14;
 
             x = /*info:DOWN_CAST_IMPLICIT*/x + z;
             x += /*info:DOWN_CAST_IMPLICIT*/z;
-            y = /*info:DOWN_CAST_IMPLICIT*/y + z;
-            y += /*info:DOWN_CAST_IMPLICIT*/z;
+            y = y + z;
+            y += z;
 
             dynamic w = 42;
             x += /*info:DYNAMIC_CAST*/w;
             y += /*info:DYNAMIC_CAST*/w;
             z += /*info:DYNAMIC_CAST*/w;
 
             A a = new A();
             B b = new B();
             var c = foo();
             a = a * b;
@@ skipping 949 matching lines @@
 
         baz1() sync* { yield* /*info:DYNAMIC_CAST*/x; }
         Iterable baz2() sync* { yield* /*info:DYNAMIC_CAST*/x; }
         Iterable<int> baz3() sync* { yield* /*warning:DOWN_CAST_COMPOSITE*/x; }
         Iterable<int> baz4() sync* { yield* bar3(); }
         Iterable<int> baz5() sync* { yield* /*info:INFERRED_TYPE_ALLOCATION*/new List(); }
     ''');
     });
   });
 }