Implement incremental tests with multiple files.

dart/tests/try/web/incremental_compilation_update_test.dart

 // Copyright (c) 2014, 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.
 
 library trydart.incremental_compilation_update_test;
 
 import 'dart:html' hide
     Element;
 
 import 'dart:async' show
@@ skipping 1631 matching lines @@
 }
 """,
 
         ],
         const <ProgramExpectation>[
             const ProgramExpectation(
                 const <String>['A(v1)']),
             const ProgramExpectation(
                 const <String>['A(v2)', 'B(v2)', 'B(A(v2))', 'A(B(v2))']),
         ]),
+
+    const EncodedResult(
+        r"""
+==> main.dart <==
+library test.main;
+
+part 'part.dart';
+==> part.dart.patch <==
+part of test.main;
+
+main() {
+<<<<<<<
+  print('Hello, World!');
+=======
+  print('Hello, Brave New World!');
+>>>>>>>
+}
+""",
+        const [
+            'Hello, World!',
+            const ProgramExpectation(
+                const <String>['Hello, Brave New World!'],
+                // TODO(ahe): Shouldn't throw.
+                compileUpdatesShouldThrow: true),
+        ]),
 ];
 
 void main() {
   listener.start();
 
   document.head.append(lineNumberStyle());
 
   summary = new SpanElement();
   document.body.append(new HeadingElement.h1()
       ..appendText("Incremental compiler tests")
@@ skipping 156 matching lines @@
 void logger(x) {
   print(x);
   bool isCheckedMode = false;
   assert(isCheckedMode = true);
   int timeout = isCheckedMode ? TIMEOUT * 2 : TIMEOUT;
   if (listener.elapsed > timeout) {
     throw 'Test timed out.';
   }
 }
 
-DivElement numberedLines(String code) {
+DivElement numberedLines(code) {
+  if (code is! Map) {
+    code = {'main.dart': code};
+  }
   DivElement result = new DivElement();
-  result.classes.add("output");
+  code.forEach((String fileName, String code) {
+    result.append(new HeadingElement.h4()..appendText(fileName));
+    DivElement lines = new DivElement();
+    result.append(lines);
+    lines.classes.add("output");
 
-  for (String text in splitLines(code)) {
-    PreElement line = new PreElement()
-        ..appendText(text.trimRight())
-        ..classes.add("line");
-    result.append(line);
-  }
-
+    for (String text in splitLines(code)) {
+      PreElement line = new PreElement()
+          ..appendText(text.trimRight())
+          ..classes.add("line");
+      lines.append(line);
+    }
+  });
   return result;
 }
 
 StyleElement lineNumberStyle() {
   StyleElement style = new StyleElement()..appendText('''
-h2, h3 {
+h2, h3, h4 {
   color: black;
 }
 
 .output {
   padding: 0px;
   counter-reset: line-number;
   padding-bottom: 1em;
 }
 
 .line {
   white-space: pre-wrap;
   padding-left: 3.5em;
   margin-top: 0;
   margin-bottom: 0;
 }
 
 .line::before {
   counter-increment: line-number;
   content: counter(line-number) " ";
   position: absolute;
   left: 0px;
   width: 3em;
   text-align: right;
   background-color: lightgoldenrodyellow;
 }
 ''');
   style.type = 'text/css';
   return style;
 }