Make large test_support targets static libraries.

chrome/test/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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/chrome_tests.gni")
 import("//chrome/common/features.gni")
 import("//chrome/test/base/js2gtest.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 # This target exists to reference other test executables to bring these files
 # into the build.
 group("test") {
   testonly = true
 }
 
 # GYP version: chrome/chrome_tests_unit.gypi:test_support_common
-source_set("test_support") {
+#
+# Use a static library here because many test binaries depend on this but don't
+# require many files from it. This makes linking more efficient.
+static_library("test_support") {
   defines = []
   testonly = true
 
   sources = [
     "base/chrome_process_util.cc",
     "base/chrome_process_util.h",
     "base/chrome_process_util_mac.cc",
     "base/chrome_render_view_host_test_harness.cc",
     "base/chrome_render_view_host_test_harness.h",
     "base/chrome_test_launcher.cc",
@@ skipping 2340 matching lines @@
 if (is_android) {
   android_library("unit_tests_java") {
     java_files = [ "android/unit_tests_apk/src/org/chromium/chrome/unit_tests_apk/ChromeNativeTestApplication.java" ]
     deps = [
       "//base:base_java",
       "//chrome/android:chrome_java",
       "//content/public/android:content_java",
     ]
   }
 }