Add precompiled headers to GN build for large targets.

build/toolchain/win/BUILD.gn

Index: build/toolchain/win/BUILD.gn
diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index 454cddea4f53249c775e17e62900a0f0a990e107..1ac362336ea783d69da3a6f0b012f4a69f073e84 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -80,9 +80,7 @@ template("msvc_toolchain") {
 
     tool("cc") {
       rspfile = "{{output}}.rsp"
-
-      # TODO(brettw) enable this when GN support in the binary has been rolled.
-      #precompiled_header_type = "msvc"
+      precompiled_header_type = "msvc"
       pdbname = "{{target_out_dir}}/{{target_output_name}}_c.pdb"
       command = "ninja -t msvc -e $env -- $cl /nologo /showIncludes /FC @$rspfile /c {{source}} /Fo{{output}} /Fd$pdbname"
       depsformat = "msvc"
@@ -95,9 +93,7 @@ template("msvc_toolchain") {
 
     tool("cxx") {
       rspfile = "{{output}}.rsp"
-
-      # TODO(brettw) enable this when GN support in the binary has been rolled.
-      #precompiled_header_type = "msvc"
+      precompiled_header_type = "msvc"
 
       # The PDB name needs to be different between C and C++ compiled files.
       pdbname = "{{target_out_dir}}/{{target_output_name}}_cc.pdb"