GTTF: Increase percentage of manual try jobs going to recipe-based trybots.

This goes from 10% to 25% .

Over Jan 9 we got 13 jobs per builder with no problems.

BUG=317931
R=joi@chromium.org

Review URL: https://codereview.chromium.org/133603003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244160 0039d316-1c4b-4281-b951-d872f2087c98

PRESUBMIT.py

@@ -1453,7 +1453,7 @@ def GetPreferredTrySlaves(project, change):
 
   # Experimental recipe-based Chromium trybots. To avoid possible capacity
   # problems, only enable for a small percentage of try runs.
-  if random.random() < 0.1:
+  if random.random() < 0.25:
     trybots.extend(GetDefaultTryConfigs([
         'linux_chromium_dbg',
         'linux_chromium_rel',