buildbucket: add longest_pending_time API

appengine/cr-buildbucket/api.py

Index: appengine/cr-buildbucket/api.py
diff --git a/appengine/cr-buildbucket/api.py b/appengine/cr-buildbucket/api.py
index 23c54a466f58b4d13da2513c5fefd51aa02e9e46..b25023608983c5b2ea86a78cfa3cd63c6c6bfeca 100644
--- a/appengine/cr-buildbucket/api.py
+++ b/appengine/cr-buildbucket/api.py
@@ -651,4 +651,26 @@ class BuildBucketApi(remote.Service):
       config_file_content=bucket.config_content,
       config_file_rev=bucket.revision,
       config_file_url=config.get_buildbucket_cfg_url(bucket.project_id),
-    )
+    )
+
+  ###########################  LONGEST_PENDING_TIME ############################
+
+  class LongestPendingTimeResponse(messages.Message):
+    longest_pending_time_sec = messages.FloatField(1)
+    error = messages.MessageField(ErrorMessage, 2)
+
+  @buildbucket_api_method(
+      endpoints.ResourceContainer(
+          message_types.VoidMessage,
+          bucket=messages.StringField(1, required=True),
+          builder=messages.StringField(2, required=True),
+      ),
+      LongestPendingTimeResponse,
+      path='metrics/longest-pending-time', http_method='GET')
+  @auth.public
+  def longest_pending_time(self, request):
+    """Returns longest pending time among all SCHEDULED builds of a builder."""
+    wait_time = service.longest_pending_time(request.bucket, request.builder)
+    return self.LongestPendingTimeResponse(
+      longest_pending_time_sec=wait_time.total_seconds(),
+    )