Windows precompiled header support in GN

build/config/BUILD.gn

 # Copyright (c) 2013 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/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
@@ skipping 378 matching lines @@
       "CoreFoundation.framework",
       "CoreGraphics.framework",
       "CoreText.framework",
       "Foundation.framework",
       "UIKit.framework",
     ]
   } else if (is_linux) {
     libs = [ "dl" ]
   }
 }
+
+# Add this config to your target to enable precompiled headers.
+#
+# On Windows, precompiled headers are done on a per-target basis. If you have
+# just a couple of files, the time it takes to precompile (~2 seconds) can
+# actually be longer than the time saved. On a Z620, a 100 file target compiles
+# about 2 seconds faster with precompiled headers, with greater savings for
+# larger targets.
+#
+# Reccommend precompiled headers for targets with more than 50 .cc files.

[scottmg, 2015/06/29 21:49:16]

"Recommend"

+config("precompiled_headers") {
+  # TODO(brettw) enable this when GN support in the binary has been rolled.
+  #if (is_win) {
+  if (false) {
+    # This is a string rather than a file GN knows about. It has to match
+    # exactly what's in the /FI flag below, and what might appear in the source
+    # code in quotes for an #include directive.
+    precompiled_header = "build/precompile.h"
+
+    # This is a file that GN will compile with the above header. It will be
+    # implicitly added to the sources (potentially multiple times, with one
+    # variant for each language used in the target).
+    precompiled_source = "//build/precompile.cc"
+
+    # Force include the header.
+    cflags = [ "/FI$precompiled_header" ]
+  }
+}