Add more diagnostics to the deferred loading implementation.

pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart

Index: pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
index faa524458558685d4939bbbc3f80cac70608733d..778f1264c0a5572f3805020f3cff41327aff5db1 100644
--- a/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
@@ -1708,8 +1708,12 @@ class Emitter extends js_emitter.EmitterBase {
           };
           // Function for initializing a loaded hunk, given its hash.
           #initializeLoadedHunk = function(hunkHash) {
-            $deferredInitializers[hunkHash](
-            #globalsHolder, ${namer.staticStateHolder});
+            var hunk = $deferredInitializers[hunkHash];
+            if (hunk == null) {

[Siggi Cherem (dart-lang), 2017/08/14 18:14:22]

technically we should never get here because I also added a check where we call
initalizeLoadedHunk

+                throw "DeferredLoading state error: code with hash '" +
+                    hunkHash + "' was not loaded";
+            }
+            hunk(#globalsHolder, ${namer.staticStateHolder});
             #deferredInitialized[hunkHash] = true;
           };
         }