Improve the error message in BuildTime.InThePast to help figure out the problem.

base/build_time.cc

Index: base/build_time.cc
diff --git a/base/build_time.cc b/base/build_time.cc
index 6f496f2efd2a9c482151911d8ecad02873935ce3..834b04120185909a489226551e3cea916b53fd28 100644
--- a/base/build_time.cc
+++ b/base/build_time.cc
@@ -14,9 +14,10 @@ namespace base {
 
 Time GetBuildTime() {
   Time integral_build_time;
-  // BUILD_DATE is exactly "Mmm DD YYYY".
-  const char kDateTime[] = BUILD_DATE " 05:00:00";
-  bool result = Time::FromUTCString(kDateTime, &integral_build_time);
+  // BUILD_DATE is exactly "Mmm DD YYYY HH:MM:SS".
+  // See //build/write_build_date_header.py. "HH:MM:SS" is normally expected to
+  // be "05:00:00" but is not enforced here.
+  bool result = Time::FromUTCString(BUILD_DATE, &integral_build_time);
   DCHECK(result);
   return integral_build_time;
 }