Enable precompiled headers for Blink on Windows

third_party/WebKit/Source/wtf/BUILD.gn

Index: third_party/WebKit/Source/wtf/BUILD.gn
diff --git a/third_party/WebKit/Source/wtf/BUILD.gn b/third_party/WebKit/Source/wtf/BUILD.gn
index 0efc9fe270a09a142b3698406a9a7a3ba1ce5795..360116fb57a01fa52133fca8c733e4afb4c3f482 100644
--- a/third_party/WebKit/Source/wtf/BUILD.gn
+++ b/third_party/WebKit/Source/wtf/BUILD.gn
@@ -1,6 +1,6 @@
 # Copyright 2014 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.
+# found in the LICENSE file.
 
 assert(!is_ios)
 
@@ -50,6 +50,7 @@ component("wtf") {
   sources = gypi_values.wtf_files
 
   configs += [
+    "//third_party/WebKit/Source:blink_pch",
     "//third_party/WebKit/Source:config",
     "//third_party/WebKit/Source:non_test_config",
   ]
@@ -121,7 +122,10 @@ test("wtf_unittests") {
     cflags = [ "/wd4068" ]  # Unknown pragma.
   }
 
-  configs += [ "//third_party/WebKit/Source:config" ]
+  configs += [
+    "//third_party/WebKit/Source:blink_pch",
+    "//third_party/WebKit/Source:config",
+  ]
 
   deps = [
     ":wtf",