Makes GetBuildTime behave identically on all build types.

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index 3bafc89ff1939bffd03a1e487233f4fd31d63a55..c35df4447239f5f2833a833833bb04bfea109cb4 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -24,6 +24,12 @@ 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"
+}
+
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
@@ -961,6 +967,7 @@ component("base") {
   public_deps = [
     ":base_paths",
     ":base_static",
+    ":build_date",
     ":debugging_flags",
   ]
 
@@ -1875,6 +1882,31 @@ test("base_unittests") {
   }
 }
 
+action("build_date") {
+  script = "//build/write_build_date_header.py"
+
+  # Force recalculation if there's been a change.
+  inputs = [
+    "//build/util/LASTCHANGE",
+  ]
+  outputs = [
+    "$target_gen_dir/generated_build_date.h",
+  ]
+
+  args =
+      [ rebase_path("$target_gen_dir/generated_build_date.h", root_build_dir) ]
+
+  if (is_official_build) {
+    args += [ "official" ]
+  } else {
+    args += [ "default" ]
+  }
+
+  if (override_build_date != "N/A") {
+    args += [ override_build_date ]
+  }
+}
+
 if (enable_nocompile_tests) {
   nocompile_test("base_nocompile_tests") {
     sources = [