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

chrome/browser/ui/BUILD.gn

Index: chrome/browser/ui/BUILD.gn
diff --git a/chrome/browser/ui/BUILD.gn b/chrome/browser/ui/BUILD.gn
index 8bfbe00146048c7636ff8402ff7a98cc1af339c3..1f9b66998cc163e653cb95430512d36a6d1a7940 100644
--- a/chrome/browser/ui/BUILD.gn
+++ b/chrome/browser/ui/BUILD.gn
@@ -20,8 +20,10 @@ config("ui_warnings") {
 }
 
 # 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.