[cr-buildbucket] Add xcode caches to ios-* builders

R=nodir@chromium.org

Bug: 731546
Change-Id: I717ac96f41c398451a2e8b888e85b6d673a7c112
Reviewed-on: https://chromium-review.googlesource.com/1035916
Commit-Queue: Sergey Berezin <sergeyberezin@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554875}

infra/config/global/cr-buildbucket.cfg

@@ -283,9 +283,19 @@ builder_mixins {
   }
 }
 
+builder_mixins {
+  name: "xcode-caches"
+  caches: {
+    # Cache for Xcode 9.2 (build version 9C40b) needed for iOS builds.
+    name: "xcode_ios_9c40b"
+    path: "xcode_ios_9c40b.app"
+  }
+}
+
 builder_mixins {
   name: "ios-ci"
   mixins: "mac-ci"
+  mixins: "xcode-caches"
   # ios bots may run both on Mac Minis with cores:4 and VMs with cores:8.
   dimensions: "cores:"
   recipe {
@@ -296,6 +306,7 @@ builder_mixins {
 builder_mixins {
   name: "ios-try"
   mixins: "mac-try"
+  mixins: "xcode-caches"
   # ios bots may run both on Mac Minis with cores:4 and VMs with cores:8.
   dimensions: "cores:"
   recipe {