Add "load from .dill" file capability and run a white-box test.

tests/compiler/dart2js/dill_loader_test.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+import 'memory_compiler.dart';
+import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/diagnostics/spannable.dart' show Spannable;
+import 'package:compiler/src/elements/entities.dart'
+    show LibraryEntity, ClassEntity;
+import 'package:compiler/src/kernel/world_builder.dart';
+import 'package:compiler/src/library_loader.dart'
+    show ScriptLoader, LibraryLoaderTask;
+import 'package:compiler/src/script.dart' show Script;
+import 'package:compiler/src/apiimpl.dart' show CompilerImpl;
+import "package:expect/expect.dart";
+import 'package:path/path.dart' as path;
+
+/// Run the dartk.dart script, and return the binary encoded results.
+List<int> runDartk(Uri filename) {
+  String basePath = path.fromUri(Platform.script);

[Johnni Winther, 2017/04/04 07:25:20]

Use `String basePath = path.fromUri(Uri.base);` and avoid the loop.

[Emily Fortuna, 2017/04/04 20:03:52]

Done.

+  while (path.basename(basePath) != 'sdk') {
+    basePath = path.dirname(basePath);
+  }
+  String dartkPath =
+      path.normalize(path.join(basePath, 'tools/dartk_wrappers/dartk'));

[Johnni Winther, 2017/04/04 07:25:20]

This won't work on Windows. I'll fix it when you land it.
'tools/dartk_wrappers/' doesn't contain a 'dartk.bat' and we don't run unittests
on Windows, anyway.

[Emily Fortuna, 2017/04/04 20:03:53]

I know, but I thought as per our discussion, that was an okay shortcoming?

[Johnni Winther, 2017/04/05 06:53:42]

Yes. I'll fix it.

+
+  var args = [filename.path, '-fbin', '-ostdout'];
+  ProcessResult result = Process.runSync(
+      dartkPath, [filename.path, '-fbin', '-ostdout'],
+      stdoutEncoding: null);
+  Expect.equals(0, result.exitCode);
+  return result.stdout;
+}
+
+class TestScriptLoader implements ScriptLoader {
+  CompilerImpl compiler;
+  TestScriptLoader(this.compiler);
+
+  Future<Script> readScript(Uri uri, [Spannable spannable]) =>
+      compiler.readScript(uri, spannable);
+}
+
+/// Test that the compiler can successfully read in .dill kernel files rather
+/// than just string source files.
+main() {
+  asyncTest(() async {
+    Uri uri = Platform.script.resolve('../../corelib/list_literal_test.dart');

[Johnni Winther, 2017/04/04 07:25:20]

Use `Uri.base.resolve('tests/corelib/list_literal_test.dart');` instead.

[Emily Fortuna, 2017/04/04 20:03:52]

Done.

+    File entity = new File.fromUri(uri);
+    DiagnosticCollector diagnostics = new DiagnosticCollector();
+    OutputCollector output = new OutputCollector();
+    Uri entryPoint = Uri.parse('memory:main.dill');
+    List<int> kernelBinary = runDartk(entity.uri);
+
+    CompilerImpl compiler = compilerFor(
+        entryPoint: entryPoint,
+        memorySourceFiles: {'main.dill': kernelBinary},
+        diagnosticHandler: diagnostics,
+        outputProvider: output,
+        options: ['--read-dill']);
+    await compiler.setupSdk();
+    LibraryLoaderTask loader = new LibraryLoaderTask(

[Johnni Winther, 2017/04/04 07:25:20]

`LibraryLoaderTask loader` -> `dynamic loader`

Then you don't need to put 'worldBuilder' in the LibraryLoaderTask interface.

[Emily Fortuna, 2017/04/04 20:03:53]

Is that really an improvement, that way we would now have no checks at all,
whereas with LibraryLoaderTask we at least know it's a LibraryLoaderTask type or
subtype.

[Johnni Winther, 2017/04/05 06:53:41]

We are relying on implementation details (that the actual type has a meaningfull
[worldBuilder] property) but that is okay in tests. `dynamic` is just a way to
circumvent the type system and avoid a warning.

+        true,
+        compiler.resolvedUriTranslator,
+        new TestScriptLoader(compiler),
+        null,
+        null,
+        null,
+        null,
+        null,
+        compiler.reporter,
+        compiler.measurer);
+
+    await loader.loadLibrary(entryPoint);
+
+    Expect.equals(0, diagnostics.errors.length);
+    Expect.equals(0, diagnostics.warnings.length);
+
+    KernelWorldBuilder worldBuilder = loader.worldBuilder;
+    LibraryEntity library = worldBuilder.lookupLibrary(uri);
+    Expect.isNotNull(library);
+    ClassEntity clss = worldBuilder.lookupClass(library, 'ListLiteralTest');
+    Expect.isNotNull(clss);
+    var member = worldBuilder.lookupClassMember(clss, 'testMain');
+    Expect.isNotNull(member);
+  });
+}