Handle local files better in server mode

lib/src/server/server.dart

Index: lib/src/server/server.dart
diff --git a/lib/src/server/server.dart b/lib/src/server/server.dart
index 555bcedf1ca60a23e51e3f0324e50589c6738530..1c563ca8a8870d6472ad58f29a2a259805aec8f8 100644
--- a/lib/src/server/server.dart
+++ b/lib/src/server/server.dart
@@ -254,17 +254,19 @@ class DevServer {
     var out = new Directory(outDir);
     if (!await out.exists()) await out.create(recursive: true);
 
-    var mainHandler =
+    var generatedHandler =
         shelf_static.createStaticHandler(outDir, defaultDocument: _entryPath);
     var sourceHandler = shelf_static.createStaticHandler(compiler.inputBaseDir,
         serveFilesOutsidePath: true);
     var topLevelHandler = (shelf.Request request) {
       var path = request.url.path;
-      if (path.endsWith('.dart')) {
-        return sourceHandler(request);
-      } else {
-        return mainHandler(request);
+      // Prefer generated code
+      var response = generatedHandler(request);
+      if (response.statusCode == 404) {

[Jennifer Messerly, 2016/01/27 20:50:02]

this feels a little bit off wrong in the architecture. Shouldn't we be able to
chain request handlers without manually checking for 404?

My understanding of Shelf is that it should support multiple kinds of handlers:
https://pub.dartlang.org/packages/shelf

Anyway, not a big deal...

+        // Fall back on original sources
+        response = sourceHandler(request);
       }
+      return response;
     };
 
     var handler = const shelf.Pipeline()