Convert some GN test support targets to static libs.

components/sessions/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 config("implementation") {
   defines = [ "SESSIONS_IMPLEMENTATION" ]
@@ skipping 111 matching lines @@
     "//components/keyed_service/core",
     "//components/variations",
     "//skia",
     "//sync",
     "//ui/base",
     "//ui/gfx",
     "//url",
   ]
 }
 
-source_set("test_support") {
+static_library("test_support") {
   testonly = true
   sources = [
     "core/serialized_navigation_entry_test_helper.cc",
     "core/serialized_navigation_entry_test_helper.h",
   ]
 
   public_deps = [
     ":sessions",
   ]
   deps = [
@@ skipping 40 matching lines @@
     "//sync",
     "//testing/gtest",
     "//ui/base",  # For page transition types.
     "//url",
   ]
 
   if (!is_ios) {
     deps += [ "//content/public/common" ]
   }
 }