dart2js: Match the runtime int is check semantics at compile time.

pkg/compiler/lib/src/constants/values.dart

Index: pkg/compiler/lib/src/constants/values.dart
diff --git a/pkg/compiler/lib/src/constants/values.dart b/pkg/compiler/lib/src/constants/values.dart
index 945aaba89e838c506dc52cca41077f467f436237..fde5cde807a91492704ee808f42a302b546c72f9 100644
--- a/pkg/compiler/lib/src/constants/values.dart
+++ b/pkg/compiler/lib/src/constants/values.dart
@@ -64,6 +64,8 @@ abstract class ConstantValue {
   bool get isMinusZero => false;
   bool get isZero => false;
   bool get isOne => false;
+  bool get isPositiveInfinity => false;
+  bool get isNegativeInfinity => false;
 
   // TODO(johnniwinther): Replace with a 'type' getter.
   DartType getType(CoreTypes types);
@@ -279,6 +281,10 @@ class DoubleConstantValue extends NumConstantValue {
 
   bool get isOne => primitiveValue == 1.0;
 
+  bool get isPositiveInfinity => primitiveValue == double.INFINITY;
+
+  bool get isNegativeInfinity => primitiveValue == -double.INFINITY;
+
   DartType getType(CoreTypes types) => types.doubleType;
 
   bool operator ==(var other) {