chromium.webkit: Adjust shard numbers for <1h cycle times.

testing/buildbot/chromium.webkit.json

Index: testing/buildbot/chromium.webkit.json
diff --git a/testing/buildbot/chromium.webkit.json b/testing/buildbot/chromium.webkit.json
index a2ab64a34ab02863256a659810abff7aeb9bc2c5..e646b469913b977bb6dc3f4b6cae072fa05c24bb 100644
--- a/testing/buildbot/chromium.webkit.json
+++ b/testing/buildbot/chromium.webkit.json
@@ -125,7 +125,7 @@
               "os": "Ubuntu-14.04"
             }
           ],
-          "shards": 6
+          "shards": 20
         }
       }
     ],
@@ -201,7 +201,7 @@
               "os": "Ubuntu-14.04"
             }
           ],
-          "shards": 6
+          "shards": 20
         }
       }
     ]
@@ -267,7 +267,7 @@
               "os": "Ubuntu-14.04"
             }
           ],
-          "shards": 6
+          "shards": 10
         }
       }
     ]
@@ -336,7 +336,7 @@
           "expiration": 36000,
           "hard_timeout": 10800,
           "io_timeout": 3600,
-          "shards": 6
+          "shards": 20
         }
       }
     ]