Add "mock" compilation feature to dart2js and use it to improve test coverage.

dart/frog/leg/emitter.dart

Index: dart/frog/leg/emitter.dart
diff --git a/dart/frog/leg/emitter.dart b/dart/frog/leg/emitter.dart
index 0a057355f354104fdb30d5954b8b02904817f3b3..034a5aba9fbfc84b48a582f3d0b51cbf23395419 100644
--- a/dart/frog/leg/emitter.dart
+++ b/dart/frog/leg/emitter.dart
@@ -653,9 +653,11 @@ function(child, parent) {
       mainEnsureGetter = "$mainAccess.$invocationName = $mainAccess";
     }
 
-  // TODO(ngeoffray): These globals are currently required by the isolate
-  // library, but since leg already generates code on an Isolate object, they
-  // are not really needed. We should remove them once Leg replaces Frog.
+    if (compiler.isMockCompilation) return "";
+
+    // TODO(ngeoffray): These globals are currently required by the isolate
+    // library, but since leg already generates code on an Isolate object, they
+    // are not really needed. We should remove them once Leg replaces Frog.
     return """
 var \$globalThis = $currentIsolate;
 var \$globalState;
@@ -692,7 +694,9 @@ ${namer.isolateAccess(isolateMain)}($mainAccess);""";
             compiler.isolateLibrary.find(Compiler.START_ROOT_ISOLATE);
         buffer.add(buildIsolateSetup(main, isolateMain));
       } else {
-        buffer.add('${namer.isolateAccess(main)}();\n');
+        if (!compiler.isMockCompilation) {

[ngeoffray, 2012/03/22 07:54:03]

I would remove this check and the one line 656, to only have one check before
emitting main (line 691).

[ahe, 2012/03/22 09:59:39]

Done.

+          buffer.add('${namer.isolateAccess(main)}();\n');
+        }
       }
       compiler.assembledCode = buffer.toString();
     });