Initialize test configuration to a default value.

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;
 
   // The URL of the current layout test.
   url.mojom.Url test_url;
 
   // True if pixel tests are enabled.
-  bool enable_pixel_dumping;
+  bool enable_pixel_dumping = true;
 
   // True if tests can open external URLs
   bool allow_external_pages;
 
   // The expected MD5 hash of the pixel results.
   string expected_pixel_hash;
 
   // The initial size of the test window.
   gfx.mojom.Size initial_size;
 };
 
 interface LayoutTestControl {
   // Asks a frame to dump its contents into a string and send them back over
   // IPC.
   LayoutDumpRequest();
 
   // Replicates test config (for an already started test) to a new renderer
   // that hosts parts of the main test window.
   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();
 };