Fix for the js-interop crash

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 0945568cfec8ca52f74c4eecf1ca669123a40266..223b688f4a6188de72069acef609c458f8fb22f3 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -5864,7 +5864,7 @@ class SsaBuilder extends ast.Visitor
         && params.optionalParametersAreNamed;
   }
 
-  HForeignCode invokeJsInteropFunction(Element element,
+  HForeignCode invokeJsInteropFunction(FunctionElement element,
                                        List<HInstruction> arguments,
                                        SourceInformation sourceInformation) {
     assert(backend.isJsInterop(element));
@@ -5918,13 +5918,13 @@ class SsaBuilder extends ast.Visitor
     var inputs = <HInstruction>[target]..addAll(arguments);
 
     js.Template codeTemplate;
+    DartType type = element.type.returnType;
     if (element.isGetter) {
       codeTemplate = js.js.parseForeignJS("#");
     } else if (element.isSetter) {
       codeTemplate = js.js.parseForeignJS("# = #");
     } else {
-      FunctionElement function = element;
-      FunctionSignature params = function.functionSignature;
+      FunctionSignature params = element.functionSignature;
 
       var argsStub = <String>[];
       for (int i = 0; i < arguments.length; i++) {
@@ -5933,17 +5933,22 @@ class SsaBuilder extends ast.Visitor
 
       if (element.isConstructor) {
         codeTemplate = js.js.parseForeignJS("new #(${argsStub.join(",")})");
+        type = element.enclosingClass.thisType;
       } else {
         codeTemplate = js.js.parseForeignJS("#(${argsStub.join(",")})");
       }
     }
 
+    // Note: here we are trusting the declared type by default to keep the
+    // codegen behavior consistent with the resolution behavior. Currently the
+    // NativeResolutionEnqueuer will trust the types by default (since this is
+    // what we always did for native APIs in dart:html). We could change both to
+    // be more conservative, but that could bring in a lot more code than what
+    // we want.

[Jacob, 2015/11/20 00:50:34]

I thought in resolution we were treating each of these methods as returning any
js class. Perhaps we should fix the bug in that direction instead of here? 

[Siggi Cherem (dart-lang), 2015/11/20 01:06:17]

Good question - we have been debating about this too. 

I like that it would make things safer, but we also were worried that if we do
that we will include everything that extends from JavaScriptObject pretty
quickly.

I just realized though that by including JavaScriptObject, you still don't bring
anything from the DOM (since those are extending directly from Interceptor) -
Stephen, if that's the case, does that lessen your worry? 

[Siggi Cherem (dart-lang), 2015/11/20 01:56:15]

I made a CL with the alternative approach, I'm still not convinced though. Here
is the link https://codereview.chromium.org/1457383003/.

If we really want tree-shaking, we could expose an interop identify function
that enables side-casts without the tree-shaking cost.

     var nativeBehavior = new native.NativeBehavior()
       ..codeTemplate = codeTemplate
-      ..typesReturned.add(
-          helpers.jsJavaScriptObjectClass.thisType)
-      ..typesInstantiated.add(
-          helpers.jsJavaScriptObjectClass.thisType)
+      ..typesReturned.add(type)
+      ..typesInstantiated.add(type)
       ..sideEffects.setAllSideEffects();
     return new HForeignCode(
         codeTemplate,