Add skia_unittests to iOS bots

BUG=460086

Review URL: https://codereview.chromium.org/959543007

Cr-Commit-Position: refs/heads/master@{#318259}

ios/build/bots/chromium.fyi/Chromium_iOS_Simulator_(dbg).json

@@ -73,6 +73,11 @@
       "app": "sql_unittests",
       "device type": "iPhone Retina (4-inch)",
       "os": "7.1"
+    },
+    {
+      "app": "skia_unittests",
+      "device type": "iPhone Retina (4-inch)",
+      "os": "7.1"
     }
   ]
 }

ios/build/bots/chromium.mac/iOS_Simulator_(dbg).json

@@ -73,6 +73,11 @@
       "app": "sql_unittests",
       "device type": "iPhone Retina (4-inch)",
       "os": "7.1"
+    },
+    {
+      "app": "skia_unittests",
+      "device type": "iPhone Retina (4-inch)",
+      "os": "7.1"
     }
   ]
 }

ios/build/bots/tryserver.chromium.mac/ios_dbg_simulator_ninja.json

@@ -73,6 +73,11 @@
       "app": "sql_unittests",
       "device type": "iPhone Retina (4-inch)",
       "os": "7.1"
+    },
+    {
+      "app": "skia_unittests",
+      "device type": "iPhone Retina (4-inch)",
+      "os": "7.1"
     }
   ]
 }