Extract interceptor calls from raw is-checks.

sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart b/sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart
index 1ea358de105955dbfad8f026270eba1da86ffdee..cc36e7280a7e853e402c395f200d724651c289e2 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart
@@ -191,6 +191,11 @@ class SsaSimplifyInterceptors extends HBaseVisitor
     } else {
       interceptedClasses = new Set<ClassElement>();
       for (var user in node.usedBy) {
+        if (user is HIs) {
+          // Is-checks can be performed on any intercepted class.
+          interceptedClasses.addAll(backend.interceptedClasses);
+          break;
+        }
         if (user is! HInvoke) continue;
         // We don't handle escaping interceptors yet.
         interceptedClasses.addAll(
@@ -248,7 +253,6 @@ class SsaSimplifyInterceptors extends HBaseVisitor
     return true;
   }
 
-  
   bool visitOneShotInterceptor(HOneShotInterceptor node) {
     HInstruction constant = tryComputeConstantInterceptor(
         node.inputs[1], node.interceptedClasses);