Make large test_support targets static libraries.

chrome/common/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/buildflag_header.gni")
 import("//chrome/common/features.gni")
 import("//chrome/version.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//tools/grit/grit_rule.gni")
 
@@ skipping 33 matching lines @@
     "ANDROID_JAVA_UI=$android_java_ui",
     "ENABLE_BACKGROUND=$enable_background",
     "ENABLE_GOOGLE_NOW=$enable_google_now",
     "ENABLE_ONE_CLICK_SIGNIN=$enable_one_click_signin",
     "ENABLE_PACKAGE_MASH_SERVICES=$enable_package_mash_services",
     "USE_VULCANIZE=$use_vulcanize",
   ]
 }
 
 # GYP version: chrome/chrome_common.gypi:common
+#
+# 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("common") {
   sources = rebase_path(gypi_values.chrome_common_sources, ".", "//chrome")
   defines = []
 
   configs += [
     "//build/config:precompiled_headers",
     "//build/config/compiler:wexit_time_destructors",
   ]
 
   public_deps = [
@@ skipping 308 matching lines @@
       "metrics_constants_util_win.h",
     ]
 
     deps = [
       "//base",
       "//chrome/installer/util:with_no_strings",
     ]
   }
 }
 
-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") {
   testonly = true
   visibility = [ "//chrome/test:test_support" ]
 
   sources = []
 
   deps = [
     ":common",
     "//base",
     "//testing/gtest",
   ]
@@ skipping 35 matching lines @@
 mojom("mojo_bindings") {
   sources = [
     "image_decoder.mojom",
     "resource_usage_reporter.mojom",
   ]
 
   public_deps = [
     "//skia/public/interfaces",
   ]
 }