Only add swiftshader/include to include_dirs on Windows.

ui/gl/init/BUILD.gn

Index: ui/gl/init/BUILD.gn
diff --git a/ui/gl/init/BUILD.gn b/ui/gl/init/BUILD.gn
index baec674031088729bae8e37946b7023683546664..f010ed0d4830431f4662437d073055f9383b6c31 100644
--- a/ui/gl/init/BUILD.gn
+++ b/ui/gl/init/BUILD.gn
@@ -18,8 +18,6 @@ component("init") {
   ]
   defines = [ "GL_INIT_IMPLEMENTATION" ]
 
-  include_dirs = [ "//third_party/swiftshader/include" ]
-
   deps = [
     "//base",
     "//ui/gfx",
@@ -35,6 +33,8 @@ component("init") {
       "gl_initializer_android.cc",
     ]
   } else if (is_win) {
+    include_dirs = [ "//third_party/swiftshader/include" ]
+
     sources += [
       "gl_factory_win.cc",
       "gl_initializer_win.cc",