Add support for Blimp engine metrics reporting in development.

components/metrics/BUILD.gn

Index: components/metrics/BUILD.gn
diff --git a/components/metrics/BUILD.gn b/components/metrics/BUILD.gn
index 6130dd5ea3ef5c2fe431768a5f86ac84c4536256..6cd7abaeff8dc42252bbe8639c675104b1549682 100644
--- a/components/metrics/BUILD.gn
+++ b/components/metrics/BUILD.gn
@@ -2,6 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+declare_args() {
+  # Overrides os name in uma metrics log to "Blimp".
+  metrics_use_blimp = false
+}
+
 # GYP version: components/metrics.gypi:metrics
 source_set("metrics") {
   sources = [
@@ -347,5 +352,12 @@ source_set("unit_tests") {
   if (is_chromeos) {
     deps += [ ":leak_detector_unit_tests" ]
   }
+
+  if (metrics_use_blimp) {
+    defines = [
+      "OVERRIDE_OS_NAME_TO_BLIMP",
+      "ENABLE_REPORTING_HEADLESS",
+    ]
+  }

[Alexei Svitkine (slow), 2016/03/07 20:38:25]

Do these same changes need to be done at the gyp level somewhere, or has the
build system completely migrated to GN at this point?

[Jess, 2016/03/07 21:09:21]

Blimp builds are entirely GN based and, for our use, gyp is entirely deprecated.
This arg should NOT be used outside blimp, but let me know if you'd prefer for
it to also appear in the gyp for the sake of consistency.

[Alexei Svitkine (slow), 2016/03/07 21:17:44]

Ah OK. Fine to keep it just in the GN file. Please add a comment above the block
about it, so it's clear to (someone like me who didn't know the above) that it's
not an accidental omission.

[Jess, 2016/03/07 22:28:08]

Done.

 }
 # TODO(GYP): metrics_chromeos