Add a "lastchange" hook.

It is used to update build/util/LASTCHANGE. This is needed because the
Chromium build tools are trying to use it to achieve a deterministic
build.

Change-Id: I28c300d48297722673cb509d97b1d71c5a8804ab
Reviewed-on: https://pdfium-review.googlesource.com/41451
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
diff --git a/DEPS b/DEPS
index 6b00f82..2b3912f 100644
--- a/DEPS
+++ b/DEPS
@@ -324,4 +324,11 @@
                 "-s", "pdfium/third_party/instrumented_libraries/binaries/msan-no-origins-trusty.tgz.sha1",
               ],
   },
+  {
+    # Update LASTCHANGE.
+    'name': 'lastchange',
+    'pattern': '.',
+    'action': ['python', 'pdfium/build/util/lastchange.py',
+               '-o', 'pdfium/build/util/LASTCHANGE'],
+  },
 ]