Update from chromium https://crrev.com/304586

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index a0cdf66228578a5818b925c1967e118895b94dda..959d4629a80a707a9c3609de9f05318d93c66473 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -399,6 +399,7 @@ component("base") {
     "metrics/histogram_delta_serialization.cc",
     "metrics/histogram_delta_serialization.",
     "metrics/histogram_flattener.h",
+    "metrics/histogram_macros.h",
     "metrics/histogram_samples.cc",
     "metrics/histogram_samples.h",
     "metrics/histogram_snapshot_manager.cc",
@@ -1402,6 +1403,11 @@ test("base_unittests") {
     sources += [ "debug/proc_maps_linux_unittest.cc" ]
     set_sources_assignment_filter(sources_assignment_filter)
   }
+
+  if (is_win) {
+    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+    cflags = [ "/wd4267" ]
+  }
 }
 
 if (is_android) {