Increase Dart's github polling interval, especially for client.dart.packages.

masters/master.client.dart.packages/master.cfg

Index: masters/master.client.dart.packages/master.cfg
diff --git a/masters/master.client.dart.packages/master.cfg b/masters/master.client.dart.packages/master.cfg
index 7c513b48a6ed92fcb869436e06e148808d3d10ab..7ee8644cdb3b4a87d498659442d8efc4a78fe294 100644
--- a/masters/master.client.dart.packages/master.cfg
+++ b/masters/master.client.dart.packages/master.cfg
@@ -121,14 +121,18 @@ c['change_source'] = [utils.get_github_poller('dart-lang', 'package-bots')]
 poller = pub_poller.PubPoller(PUBLISHED_PACKAGE_NAMES, project='pub_packages')
 c['change_source'].append(poller)
 
+interval = 300
 for package in PACKAGES:
+  interval += 7;
+  if interval > 400: interval -= 100
   if package.isGithubPackage() and package.run_tests:
     c['change_source'].append(
-        utils.get_github_poller(package.github_project, package.github_repo))
+        utils.get_github_poller(package.github_project, package.github_repo,
+                                interval=interval))
     for branch in package.extra_branches:
       c['change_source'].append(
         utils.get_github_poller(package.github_project, package.github_repo,
-                                branch))
+                                branch, interval=interval))
 
 ####### BUILDSLAVES
 
@@ -177,7 +181,7 @@ if MAIL_NOTIFIER:
 c['buildHorizon'] = 1000
 c['logHorizon'] = 500
 # Must be at least 2x the number of slaves.
-c['eventHorizon'] = 200
+c['eventHorizon'] = 600
 
 # Template generation is using 40 entries, so give it a little extra.
 c['buildCacheSize'] = 42