Refactor Library/CompilationUnit and how we define local Scope.

lib/compiler/implementation/scanner/listener.dart

Index: lib/compiler/implementation/scanner/listener.dart
diff --git a/lib/compiler/implementation/scanner/listener.dart b/lib/compiler/implementation/scanner/listener.dart
index 9ffe69c5350655b9eda0725c427dfeb58f0e60e2..a6c8d782fc6b25030a5ae2f1e07fd673c6f15c77 100644
--- a/lib/compiler/implementation/scanner/listener.dart
+++ b/lib/compiler/implementation/scanner/listener.dart
@@ -556,10 +556,14 @@ class ElementListener extends Listener {
     }
     StringNode firstArgument = popLiteralString();
     Identifier tag = popNode();
-    compilationUnitElement.addTag(new ScriptTag(tag, firstArgument,
-                                                argumentName, prefix,
-                                                beginToken, endToken),
-                                  listener);
+    LibraryElement library = compilationUnitElement.getLibrary();
+    if (library.entryCompilationUnit != compilationUnitElement) {
+      // Only allow script tags in the entry compilation unit.
+      listener.cancel("script tags not allowed here", node: tag);
+    }
+    ScriptTag scriptTag = new ScriptTag(tag, firstArgument, argumentName,
+                                        prefix, beginToken, endToken);
+    library.addTag(scriptTag, listener);
   }
 
   void endClassDeclaration(int interfacesCount, Token beginToken,