Make source information on conditions mandatory in CPS

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

Index: pkg/compiler/lib/src/cps_ir/cps_fragment.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_fragment.dart b/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
index c84e9a97a48388c784e1e1c2376374d47ffed142..903b672bbe8bca3c8e4a2635f28247c0f85de1c8 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
@@ -200,7 +200,8 @@ class CpsFragment {
     Continuation trueCont = new Continuation(<Parameter>[]);
     Continuation falseCont = new Continuation(<Parameter>[]);
     put(new LetCont.two(trueCont, falseCont,
-            new Branch(condition, trueCont, falseCont, strict: strict)));
+            new Branch(condition, trueCont, falseCont,
+                       sourceInformation, strict: strict)));
     if (negate) {
       context = trueCont;
       return new CpsFragment(sourceInformation, falseCont);