Get headless_shell building on Windows.

headless/BUILD.gn

Index: headless/BUILD.gn
diff --git a/headless/BUILD.gn b/headless/BUILD.gn
index cea651df4c5d40fc1db2c12dd2b8a20c4e7f6c65..692e6a5079f09256e2db8e622c0ca749ae95b0c0 100644
--- a/headless/BUILD.gn
+++ b/headless/BUILD.gn
@@ -299,14 +299,6 @@ static_library("headless_lib") {
     "//url",
   ]
 
-  if (is_win) {
-    deps += [
-      "//build/win:default_exe_manifest",
-      "//content:sandbox_helper_win",
-      "//sandbox",
-    ]
-  }
-
   if (!is_mac) {
     deps += [ "//ui/aura" ]
   }
@@ -459,6 +451,14 @@ executable("headless_shell") {
     "//headless:headless_shell_lib",
   ]
 
+  if (is_win) {
+    deps += [
+      "//build/win:default_exe_manifest",
+      "//content:sandbox_helper_win",
+      "//sandbox",
+    ]
+  }
+
   configs += [ ":headless_implementation" ]
 }