Docserver: Default to master commit ID on refresh

Currently _refresh handler caches data uses tip of tree
and caches data under the remote's master commit ID if
run without a 'commit' paramter.

This CL changes the handler to use the last cached 'master'
commit ID instead, so that refresh tasks for non-chromium-git
data can be run between refresh cycles.

BUG=None
R=kalman@chromium.org
NOTRY=True

Review URL: https://codereview.chromium.org/684113003

Cr-Commit-Position: refs/heads/master@{#302635}

chrome/common/extensions/docs/server2/app.yaml

 application: chrome-apps-doc
-version: 3-47-1
+version: 3-47-2
 runtime: python27
 api_version: 1
 threadsafe: false

chrome/common/extensions/docs/server2/cron.yaml

@@ -2,4 +2,4 @@ cron:
 - description: Repopulates all cached data.
   url: /_cron
   schedule: every 60 minutes
-  target: 3-47-1
+  target: 3-47-2

chrome/common/extensions/docs/server2/refresh_servlet.py

@@ -90,6 +90,12 @@ class RefreshServlet(Servlet):
     commit_tracker = CommitTracker(server_instance.object_store_creator)
     refresh_tracker = RefreshTracker(server_instance.object_store_creator)
 
+    # If no commit was given, use the ID of the last cached master commit.
+    # This allows sources external to the chromium repository to be updated
+    # independently from individual refresh cycles.
+    if commit is None:
+      commit = commit_tracker.Get('master').Get()
+
     success = True
     try:
       if source_name == 'platform_bundle':

chrome/common/extensions/docs/server2/rietveld_patcher.py

@@ -52,8 +52,8 @@ class RietveldPatcher(Patcher):
       raise RietveldPatcherError('Cannot parse issue %s.' % self._issue)
 
     if not issue_json.get('base_url') in _CHROMIUM_REPO_BASEURLS:
-      raise RietveldPatcherError('Issue %s\'s base url is unknown.' %
-          self._issue)
+      raise RietveldPatcherError('Issue %s\'s base url (%s) is unknown.' %
+          (self._issue, issue_json.get('base_url')))
 
     return str(patchsets[-1])