Proof of concept of unity build for WebKit/Source/core/html

third_party/WebKit/Source/core/html/BUILD.gn

-# Copyright 2016 The Chromium Authors. All rights reserved.
+# 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.
 
 import("//build/split_static_library.gni")
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("html") {
+
+  unity_build = true
+  if (unity_build) {
+    sources = [ "all_html_files.cpp" ]
+  } else {
   split_count = 5
-
   sources = [
     "AutoplayUmaHelper.cpp",
     "AutoplayUmaHelper.h",
     "ClassList.cpp",
     "ClassList.h",
     "CrossOriginAttribute.cpp",
     "CrossOriginAttribute.h",
     "DocumentNameCollection.cpp",
     "DocumentNameCollection.h",
     "Float32ImageData.cpp",
@@ skipping 485 matching lines @@
     "track/vtt/VTTParser.cpp",
     "track/vtt/VTTParser.h",
     "track/vtt/VTTRegion.cpp",
     "track/vtt/VTTRegion.h",
     "track/vtt/VTTScanner.cpp",
     "track/vtt/VTTScanner.h",
     "track/vtt/VTTToken.h",
     "track/vtt/VTTTokenizer.cpp",
     "track/vtt/VTTTokenizer.h",
   ]
-
+}
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }