Layout tests: Enable fetching generated files from the build directory

content/shell/common/layout_test.mojom

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module content.mojom;
 
 import "mojo/common/file_path.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 import "url/mojo/url.mojom";
 
 struct ShellTestConfiguration {
   // The current working directory.
   mojo.common.mojom.FilePath current_working_directory;
 
   // The temporary directory of the system.
   mojo.common.mojom.FilePath temp_path;
 
+  // The build directory.
+  mojo.common.mojom.FilePath build_directory;
+

[qyearsley, 2017/03/20 17:40:00]

In general, what does this file control? Is ShellTestConfiguration something
that is always set up when running content_shell?

[yzshen1, 2017/03/20 18:01:04]

This is the layout test configuration information sending from the browser to
the renderer process.

It is only set up when running layout tests.

   // The URL of the current layout test.
   url.mojom.Url test_url;
 
   // True if pixel tests are enabled.
   bool enable_pixel_dumping;
 
   // True if tests can open external URLs
   bool allow_external_pages;
 
   // The expected MD5 hash of the pixel results.
@@ skipping 13 matching lines @@
   ReplicateTestConfiguration(ShellTestConfiguration config);
 
   // Sets the test config for a layout test that is being started.  This message
   // is sent only to a renderer that hosts parts of the main test window.
   SetTestConfiguration(ShellTestConfiguration config);
 
   // Sets up a secondary renderer (renderer that doesn't [yet] host parts of the
   // main test window) for a layout test.
   SetupSecondaryRenderer();
 };