Adds ability to specify how aura::Env is created in content

content/public/common/BUILD.gn

Index: content/public/common/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index c0a8a030feb4edcd6d5b59ad79f05a14c08784e7..dc256d587b362f8d1e8f4bda9cf88185d7211141 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -5,6 +5,7 @@
 import("//build/buildflag_header.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/features.gni")
+import("//build/config/ui.gni")
 import("//media/media_options.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//ppapi/features/features.gni")
@@ -273,6 +274,10 @@ source_set("common_sources") {
     "//ui/gfx/ipc/skia",
   ]
 
+  if (use_aura) {
+    deps += [ "//ui/aura" ]
+  }
+
   # //content/common needs to include public headers.
   allow_circular_includes_from = [
     "//content/common",