Make chrome/browser/ui a source set on 64-bit official builds.

chrome/browser/ui/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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
 
 gypi_values = exec_script("//build/gypi_to_gn.py",
                           [ rebase_path("../../chrome_browser_ui.gypi") ],
                           "scope",
                           [ "../../chrome_browser_ui.gypi" ])
 
 config("ui_warnings") {
   if (is_clang) {
     # TODO(thakis): Remove this once http://crbug.com/383820 is figured out
     cflags = [ "-Wno-nonnull" ]
   }
 }
 
 # 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.
-if (is_mac) {
+# require many files from it. This makes linking more efficient. However, on
+# x64 official builds the static library will be too large (> 32-bits) so use
+# source sets in that case.
+if (is_mac || (current_cpu == "x64" && is_official_build)) {
   # TODO(brettw) bug 618797: On Mac making this target a static_library causes
   # a crash on startup and the browser_tests all fail. My guess is this is due
   # to a required static initializer not being brought in.
   chrome_browser_target_type = "source_set"
 } else {
   chrome_browser_target_type = "static_library"
 }
 target(chrome_browser_target_type, "ui") {
   sources = []
   defines = []
@@ skipping 672 matching lines @@
     "//chrome/browser",
     "//content/public/browser",
     "//content/public/common",
     "//content/test:test_support",
     "//net:test_support",
     "//skia",
     "//testing/gtest",
     "//ui/base",
   ]
 }