dart2js cps_ir: Use interceptors for is-checks.

pkg/compiler/lib/src/cps_ir/builtin_operator.dart

Index: pkg/compiler/lib/src/cps_ir/builtin_operator.dart
diff --git a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
index 28397eb68bc52a7f7558c4a456f6ffb850a98cc7..6dabc1f6179dc6c93bbbfd98b0c0d8d23580293b 100644
--- a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
+++ b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
@@ -103,6 +103,37 @@ enum BuiltinOperator {
   ///
   /// Compiles to `typeof x === 'number' && Math.floor(x) === x`
   IsNumberAndFloor,
+
+  /// Returns true if the argument is a fixed length Array.
+  ///
+  /// Uses one argument.
+  ///
+  /// Precondition: Argument is a JavaScript Array.

[sra1, 2015/10/06 06:47:58]

I'm pretty sure there are some places where this is not true.
However, this is no worse than what it is replacing.

+  IsFixedLengthJSArray,
+
+  // TODO(sra): Remove this and replace with IsFalsy(IsFixedLengthJSArray(x)).
+  IsExtendableJSArray,
+
+  /// Returns true if the argument is an unmodifiable Array.
+  ///
+  /// Uses one argument.
+  ///
+  /// Precondition: Argument is a JavaScript Array.
+  IsUnmodifiableJSArray,
+
+  // TODO(sra): Remove this and replace with IsFalsy(IsUnmodifiableArray(x)).
+  IsModifiableJSArray,
+
+
+  /// Compiles to
+  ///
+  ///     typeof x === 'object' && x !== null && x.constructor === Array
+  ///
+  /// TODO(sra): Break into individual tests.
+  IsJSArray,
+  ISJSArrayNotNull,
+  IsJSArrayObject,
+  IsJSArrayConstructor,
 }
 
 /// A method supported natively in the CPS and Tree IRs using the