[Android] Add support for external sharding to the test runner.

testing/buildbot/chromium.swarm.json

Index: testing/buildbot/chromium.swarm.json
diff --git a/testing/buildbot/chromium.swarm.json b/testing/buildbot/chromium.swarm.json
index 70f448cd81e0b64b85440a6717a1ea94853619ac..26fa62408f98b593cc6e6a6cb2c7f42c70fbd94b 100644
--- a/testing/buildbot/chromium.swarm.json
+++ b/testing/buildbot/chromium.swarm.json
@@ -13,7 +13,8 @@
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
-          ]
+          ],
+          "shards": 7
         },
         "test": "android_webview_test_apk"
       },
@@ -42,7 +43,8 @@
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
-          ]
+          ],
+          "shards": 14
         },
         "test": "chrome_public_test_apk"
       },
@@ -55,7 +57,8 @@
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
-          ]
+          ],
+          "shards": 10
         },
         "test": "content_browsertests"
       },
@@ -68,7 +71,8 @@
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
-          ]
+          ],
+          "shards": 3
         },
         "test": "content_unittests"
       },
@@ -81,7 +85,8 @@
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
-          ]
+          ],
+          "shards": 4
         },
         "test": "net_unittests"
       },
@@ -94,7 +99,8 @@
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
-          ]
+          ],
+          "shards": 5
         },
         "test": "unit_tests"
       }
@@ -114,7 +120,8 @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
-          ]
+          ],
+          "shards": 7
         },
         "test": "android_webview_test_apk"
       },
@@ -143,7 +150,8 @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
-          ]
+          ],
+          "shards": 15
         },
         "test": "chrome_public_test_apk"
       },
@@ -156,7 +164,8 @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
-          ]
+          ],
+          "shards": 10
         },
         "test": "content_browsertests"
       },
@@ -169,7 +178,8 @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
-          ]
+          ],
+          "shards": 4
         },
         "test": "content_unittests"
       },
@@ -182,7 +192,8 @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
-          ]
+          ],
+          "shards": 4
         },
         "test": "net_unittests"
       },
@@ -195,7 +206,8 @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
-          ]
+          ],
+          "shards": 8
         },
         "test": "unit_tests"
       }