Add version validation for LookupMap, also add unittest directly in LookupMap.

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 2ab5920b541b21c97991e70f1a6db03325974555..e0311003aa1ea7cc2d8f6b729899b67a1b3e0e45 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -2159,7 +2159,7 @@ class JavaScriptBackend extends Backend {
       } else if (uri == Uris.dart_html) {
         htmlLibraryIsLoaded = true;
       } else if (uri == PACKAGE_LOOKUP_MAP) {
-        lookupMapAnalysis.initRuntimeClass(find(library, 'LookupMap'));
+        lookupMapAnalysis.init(library);
       }
       annotations.onLibraryScanned(library);
     });
@@ -2605,7 +2605,13 @@ class JavaScriptBackend extends Backend {
     return true;
   }
 
-  void onQueueClosed() => lookupMapAnalysis.onQueueClosed();
+  void onQueueClosed() {
+    lookupMapAnalysis.onQueueClosed();
+  }
+
+  void onCodegenStart() {
+    lookupMapAnalysis.onCodegenStart();
+  }
 
   void onElementResolved(Element element, TreeElements elements) {
     if ((element.isFunction || element.isGenerativeConstructor) &&