New Relic metric: Enrolled courses on dashboard.

This is so we can better map how student dashboard performance maps to
number of enrolled courses.

common/djangoapps/student/views.py

@@ -118,6 +118,8 @@ from openedx.core.djangoapps.embargo import api as embargo_api
 import analytics
 from eventtracking import tracker
 
+import newrelic_custom_metrics
+
 # Note that this lives in LMS, so this dependency should be refactored.
 from notification_prefs.views import enable_notifications
 
@@ -615,6 +617,10 @@ def dashboard(request):
     # enrollments, because it could have been a data push snafu.
     course_enrollments = list(get_course_enrollments(user, course_org_filter, org_filter_out_set))
 
+    # Record how many courses there are so that we can get a better
+    # understanding of usage patterns on prod.
+    newrelic_custom_metrics.accumulate('num_courses', len(course_enrollments))
+
     # sort the enrollment pairs by the enrollment date
     course_enrollments.sort(key=lambda x: x.created, reverse=True)