Update mock SDK 'double'.

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

Index: pkg/analyzer/test/src/task/strong/checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/checker_test.dart b/pkg/analyzer/test/src/task/strong/checker_test.dart
index 28ab23aa81a90a172b1a8dbc7725a5d356d6de3b..5fbc192248eaba9f57ec8806423490dce6dd990b 100644
--- a/pkg/analyzer/test/src/task/strong/checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/checker_test.dart
@@ -2051,7 +2051,7 @@ void main() {
       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) {}
      }
@@ -2343,8 +2343,8 @@ void main() {
 
             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;