Fix ENABLE_SWIFTSHADER flag.

ui/gl/BUILD.gn

Index: ui/gl/BUILD.gn
diff --git a/ui/gl/BUILD.gn b/ui/gl/BUILD.gn
index bc11394c49c611517446fc22cd23338a1a858942..d34c5aba2d31f7ee7b3cfdb87f656aaa6ec72c72 100644
--- a/ui/gl/BUILD.gn
+++ b/ui/gl/BUILD.gn
@@ -2,10 +2,16 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/buildflag_header.gni")
+import("//build/config/chrome_build.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
+declare_args() {
+  enable_swiftshader = is_chrome_branded && is_win

[Nico, 2016/09/15 15:47:33]

could we start with this set to false, and then flip this in a separate cl?
as-is, the cl description sounds like this just adds a flag, not that it
actually changes behavior on windows

also, why do we enable this only in branded builds? we try to keep chromium and
chrome as similar as possible (but i suppose that's a question for the follow-up
with the actual switch)

+}
+
 use_egl = is_win || is_android || is_linux
 use_glx = use_x11
 
@@ -14,6 +20,11 @@ if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
+buildflag_header("gl_features") {
+  header = "gl_features.h"
+  flags = [ "ENABLE_SWIFTSHADER=$enable_swiftshader" ]
+}
+
 config("gl_config") {
   defines = []
   if (use_glx) {