Add iOS compile bot to the CQ

BUG=skia:4252

Review URL: https://codereview.chromium.org/1501453005
diff --git a/infra/branch-config/cq.cfg b/infra/branch-config/cq.cfg
index 2fb1ff3..35a5fda 100644
--- a/infra/branch-config/cq.cfg
+++ b/infra/branch-config/cq.cfg
@@ -32,6 +32,7 @@
     buckets {
       name: "client.skia.compile"
       builders { name: "Build-Mac10.8-Clang-x86_64-Release-Trybot" }
+      builders { name: "Build-Mac10.9-Clang-Arm7-Debug-iOS-Trybot" }
       builders { name: "Build-Ubuntu-Clang-x86_64-Debug-Trybot" }
       builders { name: "Build-Ubuntu-GCC-Arm64-Debug-Android-Trybot" }
       builders { name: "Build-Ubuntu-GCC-Arm7-Debug-Android-Trybot" }