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

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

Index: third_party/WebKit/Source/core/html/BUILD.gn
diff --git a/third_party/WebKit/Source/core/html/BUILD.gn b/third_party/WebKit/Source/core/html/BUILD.gn
index 4ab90bb0827c7022f6019055522acdaf12a544d8..6413053eb2f3cefaaf22fc053232a67078e1ad24 100644
--- a/third_party/WebKit/Source/core/html/BUILD.gn
+++ b/third_party/WebKit/Source/core/html/BUILD.gn
@@ -1,4 +1,4 @@
-# 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.
 
@@ -6,8 +6,12 @@ import("//build/split_static_library.gni")
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("html") {
-  split_count = 5
 
+  unity_build = true
+  if (unity_build) {
+    sources = [ "all_html_files.cpp" ]
+  } else {
+  split_count = 5
   sources = [
     "AutoplayUmaHelper.cpp",
     "AutoplayUmaHelper.h",
@@ -513,7 +517,7 @@ blink_core_sources("html") {
     "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",