Add a simple "user stats" extension that uses the new infobox features.

This change adds a new extension that populates the extra section of the user
infobox with counts of that user's incoming and outgoing review requests.

Testing done:
Installed and enabled the extension. Hovered over a user and saw counts of
their incoming and outgoing review requests.

Reviewed at https://reviews.reviewboard.org/r/8080/

rb_user_stats/rb_user_stats/extension.py

@@ -0,0 +1,72 @@
+from __future__ import unicode_literals
+
+import time
+
+from django.utils import six
+from reviewboard.extensions.base import Extension
+from reviewboard.extensions.hooks import UserInfoboxHook
+from reviewboard.reviews.models import ReviewRequest
+
+
+class UserStatsInfoboxHook(UserInfoboxHook):
+    """Add user statistics to the infobox."""
+
+    def get_etag_data(self, user, request, local_site):
+        """Return data to include in the ETag calculation.
+
+        When this extension is enabled, we don't want the browser to cache
+        anything, because we don't save any work by doing so. Just return a
+        cache-busting timestamp.
+
+        Args:
+            user (django.contrib.auth.models.User):
+                The user whose infobox is being shown.
+
+            request (django.http.HttpRequest):
+                The request object.
+
+            local_site (reviewboard.site.models.LocalSite):
+                The current local site, if any.
+
+        Returns:
+            six.text_type:
+            Data to include in the ETag.
+        """
+        return six.text_type(time.time())
+
+    def get_extra_context(self, user, request, local_site):
+        """Return context to include when rendering the template.
+
+        Args:
+            user (django.contrib.auth.models.User):
+                The user whose infobox is being shown.
+
+            request (django.http.HttpRequest):
+                The request object.
+
+            local_site (reviewboard.site.models.LocalSite):
+                The current local site, if any.
+
+        Returns:
+            dict:
+            Additional data to include when rendering the template.
+        """
+        return {
+            'incoming': ReviewRequest.objects.to_user(
+                user, user=request.user, local_site=local_site).count(),
+            'outgoing': ReviewRequest.objects.from_user(
+                user, user=request.user, local_site=local_site).count(),
+        }
+
+
+class RBUserStats(Extension):
+    """The user statistics extension."""
+
+    metadata = {
+        'Name': 'rb-user-stats',
+        'Summary': 'Show statistics for Review Board users in the infobox',
+    }
+
+    def initialize(self):
+        """Initialize the extension."""
+        UserStatsInfoboxHook(self, 'rb-user-stats-infobox.html')

rb_user_stats/rb_user_stats/templates/rb-user-stats-infobox.html

@@ -0,0 +1,2 @@
+<p>Outgoing Review Requests: {{outgoing}}</p>
+<p>Incoming Review Requests: {{incoming}}</p>

rb_user_stats/setup.py

@@ -0,0 +1,28 @@
+from __future__ import unicode_literals
+
+from reviewboard.extensions.packaging import setup
+
+
+PACKAGE = 'rb-user-stats'
+VERSION = '0.1'
+
+setup(
+    name=PACKAGE,
+    version=VERSION,
+    description='Show statistics for Review Board users in the infobox',
+    url='https://www.reviewboard.org/',
+    author='Beanbag, Inc.',
+    author_email='[email protected]',
+    maintainer='Beanbag, Inc.',
+    maintainer_email='[email protected]',
+    packages=['rb_user_stats'],
+    entry_points={
+        'reviewboard.extensions':
+            '%s = rb_user_stats.extension:RBUserStats' % PACKAGE,
+    },
+    package_data={
+        b'rb_user_stats': [
+            'templates/rb_user_stats/*.html',
+        ],
+    }
+)