dart2js: Store mapTypeToInterceptor in embedded global.

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

Index: pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
index a69fc80565b7fa30472c8a07e3c96139606f889e..bb8be20724638e180eccb958ed8a99b6f9ff7708 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
@@ -770,8 +770,6 @@ class OldEmitter implements Emitter {
     for (Element element in Elements.sortedByPosition(staticNonFinalFields)) {
       // [:interceptedNames:] is handled in [emitInterceptedNames].
       if (element == backend.interceptedNames) continue;
-      // `mapTypeToInterceptor` is handled in [emitMapTypeToInterceptor].
-      if (element == backend.mapTypeToInterceptor) continue;
       compiler.withCurrentElement(element, () {
         jsAst.Expression initialValue;
         if (outputUnit !=