Fix gn bootstrap

R=dpranke

Change-Id: I9f93686d2bab2d3625363142bb05349817e1c5b5
Reviewed-on: https://chromium-review.googlesource.com/982250
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#546160}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c89b8fabf7a9234c9d073cad1e5931d10fa28a34

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index 2bf25e5..8096364 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -486,6 +486,7 @@
       'base/message_loop/message_pump.cc',
       'base/message_loop/message_pump_default.cc',
       'base/metrics/bucket_ranges.cc',
+      'base/metrics/dummy_histogram.cc',
       'base/metrics/field_trial.cc',
       'base/metrics/field_trial_param_associator.cc',
       'base/metrics/field_trial_params.cc',