ceil/floor/truncate/round return integers.

sdk/lib/_internal/compiler/implementation/js_backend/constant_system_javascript.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.
 
 part of js_backend;
 
 const JAVA_SCRIPT_CONSTANT_SYSTEM = const JavaScriptConstantSystem();
 
 class JavaScriptBitNotOperation extends BitNotOperation {
   const JavaScriptBitNotOperation();
@@ skipping 181 matching lines @@
       IntConstant intConstant = constant;
       int intValue = intConstant.value;
       if (!integerFitsIntoDouble(intValue)) {
         return new DoubleConstant(intValue.toDouble());
       }
     } else if (constant.isDouble()) {
       DoubleConstant doubleResult = constant;
       double doubleValue = doubleResult.value;
       if (!doubleValue.isInfinite && !doubleValue.isNaN &&
           !constant.isMinusZero()) {
-        int intValue = doubleValue.toInt();
+        int intValue = doubleValue.truncate();
         if (intValue == doubleValue && integerFitsIntoDouble(intValue)) {
           return new IntConstant(intValue);
         }
       }
     }
     return constant;
   }
 
   NumConstant createInt(int i)
       => convertToJavaScriptConstant(new IntConstant(i));
@@ skipping 17 matching lines @@
     // At runtime, an integer is both an integer and a double: the
     // integer type check is Math.floor, which will return true only
     // for real integers, and our double type check is 'typeof number'
     // which will return true for both integers and doubles.
     if (s.element == compiler.intClass && t.element == compiler.doubleClass) {
       return true;
     }
     return compiler.types.isSubtype(s, t);
   }
 }