For Doubl erounding call C-function instead of attempting to inline it. Fixes issue 8760.

tests/language/arithmetic_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.
 // Dart test program to test arithmetic operations.
 
 library arithmetic_test;
 import 'dart:math';
 
 class ArithmeticTest {
 
@@ skipping 261 matching lines @@
     // Smi.
     Expect.equals(0, (0).round());
     Expect.equals(1, (1).round());
     Expect.equals(-1, (-1).round());
     // Big.
     Expect.equals(big, big.round());
     Expect.equals(-big, (-big).round());
     // Double.
     Expect.equals(3.0, (2.6).round());
     Expect.equals(-3.0, (-2.6).round());
+    Expect.equals(3.0, (2.5).round());
+    Expect.equals(-3.0, (-2.5).round());
     Expect.equals(0.0, (0.0).round());
     Expect.equals(0.0, (0.1).round());
     Expect.equals(false, (0.0).round().isNegative);
     Expect.equals(false, (0.1).round().isNegative);
     Expect.equals(-0.0, (-0.0).round());
     Expect.equals(-0.0, (-0.3).round());
     Expect.equals(2.0, (2.1).round());
     Expect.equals(-2.0, (-2.1).round());
     Expect.equals(1.0, (0.5).round());
     Expect.equals(0.0, (0.49999999999999994).round());
@@ skipping 146 matching lines @@
       runOne();
       testSmiDivDeopt();
       testSqrtDeopt();
     }
   }
 }
 
 main() {
   ArithmeticTest.testMain();
 }