Bug 1244143 - Record whether or not an artifact build was used in build telemetry data r=gps

This adds a substs field and cherrypicks the MOZ_ARTIFACT_BUILDS field so
we can determine whether or not an artifact build occurred.

MozReview-Commit-ID: 8aio8mP8pmR

--HG--
extra : rebase_source : aa0dc2b7ef61e8b02d202c3a631d276e019d3dfd

python/mozbuild/mozbuild/mach_commands.py

@@ -495,8 +495,21 @@ class Build(MachCommandBase):
 
             telemetry_handler = getattr(self._mach_context,
                                         'telemetry_handler', None)
-            usage = monitor.record_resource_usage()
-            telemetry_handler(self._mach_context, usage)
+            telemetry_data = monitor.record_resource_usage()
+
+            # Record build configuration data. For now, we cherry pick
+            # items we need rather than grabbing everything, in order
+            # to avoid accidentally disclosing PII.
+            try:
+                moz_artifact_builds = self.substs.get('MOZ_ARTIFACT_BUILDS',
+                                                      False)
+                telemetry_data['substs'] = {
+                    'MOZ_ARTIFACT_BUILDS': moz_artifact_builds,
+                }
+            except BuildEnvironmentNotFoundException:
+                pass
+
+            telemetry_handler(self._mach_context, telemetry_data)
 
         # Only for full builds because incremental builders likely don't
         # need to be burdened with this.