cps-ir: Add support for intercepted calls.

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
index b4f111a98f3607b3778de5dc8cc8020083b9d610..413f0e1201a938405e47876168ca53ed228ade35 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
@@ -208,6 +208,8 @@ class InvokeMethod extends Expression implements Invoke {
            (selector.kind == SelectorKind.INDEX && arguments.length == 2));
   }
 
+  bool get isIntercepted => receiver.definition is Interceptor;
+
   accept(Visitor visitor) => visitor.visitInvokeMethod(this);
 }
 
@@ -455,6 +457,14 @@ class Identical extends Primitive {
   accept(Visitor visitor) => visitor.visitIdentical(this);
 }
 
+class Interceptor extends Primitive {
+  final Reference<Primitive> input;
+  final Set<ClassElement> interceptedClasses;
+  Interceptor(Primitive input, this.interceptedClasses)
+      : this.input = new Reference<Primitive>(input);
+  accept(Visitor visitor) => visitor.visitInterceptor(this);
+}
+
 class Constant extends Primitive {
   final ConstantExpression expression;
 
@@ -690,6 +700,7 @@ abstract class Visitor<T> {
 
   // JavaScript specific nodes.
   T visitIdentical(Identical node) => visitPrimitive(node);
+  T visitInterceptor(Interceptor node) => visitPrimitive(node);
 }
 
 /// Recursively visits the entire CPS term, and calls abstract `process*`
@@ -879,6 +890,12 @@ abstract class RecursiveVisitor extends Visitor {
     processReference(node.left);
     processReference(node.right);
   }
+
+  processInterceptor(Interceptor node) {}
+  visitInterceptor(Interceptor node) {
+    processInterceptor(node);
+    processReference(node.input);
+  }
 }
 
 /// Keeps track of currently unused register indices.
@@ -1063,5 +1080,8 @@ class RegisterAllocator extends Visitor {
     visitReference(node.left);
     visitReference(node.right);
   }
-}
 
+  void visitInterceptor(Interceptor node) {
+    visitReference(node.input);
+  }
+}