Makes GetBuildTime behave identically on all build types.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
 #
 # Since base includes so many low-level things that vary widely and
 # unpredictably for the various build types, we prefer a slightly different
 # style. Instead, there are big per-platform blocks of inclusions and
 # exclusions. If a given file has an inclusion or exclusion rule that applies
 # for multiple conditions, perfer to duplicate it in both lists. This makes it
 # a bit easier to see which files apply in which cases rather than having a
 # huge sequence of random-looking conditionals.
 
 import("//build/buildflag_header.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/config/ui.gni")
 import("//build/nocompile.gni")
 import("//testing/test.gni")
 
+declare_args() {
+  # Override this value to give a specific build date.
+  # See //base/build_time.cc for more details.
+  override_build_date = "N/A"

[M-A Ruel, 2016/01/30 02:58:14]

What about:

- By default override_build_date is set to the first of the month. This means
normal builds will be deterministic for the month only. This means that on the
first of each month, the cache will be invalidated, causing significant load. :/
- On official build, override_build_date defaults to "N/A".

[Zachary Forman, 2016/02/01 07:28:30]

I like this - we could actually use a python script, and actually use 'real'
UTC, as well.

+}
+
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 config("base_flags") {
   if (is_clang) {
     cflags = [
       # Don't die on dtoa code that uses a char as an array index.
       # This is required solely for base/third_party/dmg_fp/dtoa_wrapper.cc.
       "-Wno-char-subscripts",
@@ skipping 1273 matching lines @@
       data += [ "//third_party/llvm-build/Release+Asserts/bin/llvm-symbolizer" ]
     }
   }
 
   configs += [ "//build/config/compiler:wexit_time_destructors" ]
   if (!is_debug) {
     configs -= [ "//build/config/compiler:default_optimization" ]
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 
+  if (override_build_date != "N/A") {
+    defines += [ "BUILD_TIME=\"" + override_build_date + "\"" ]
+  }
+
   allow_circular_includes_from = public_deps
 }
 
 buildflag_header("debugging_flags") {
   header = "debugging_flags.h"
   header_dir = "base/debug"
   flags = [ "ENABLE_PROFILING=$enable_profiling" ]
 }
 
 # This is the subset of files from base that should not be used with a dynamic
@@ skipping 810 matching lines @@
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }