Split up ios/web:test_support.

ios/chrome/browser/snapshots/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("snapshots") {
   sources = [
     "lru_cache.h",
     "lru_cache.mm",
     "snapshot_cache.h",
     "snapshot_cache.mm",
@@ skipping 36 matching lines @@
   sources = [
     "lru_cache_unittest.mm",
     "snapshot_cache_unittest.mm",
     "snapshots_util_unittest.mm",
   ]
   deps = [
     ":snapshots",
     "//base",
     "//ios/chrome/browser/ui",
     "//ios/web",
-    "//ios/web:test_support",
+    "//ios/web/public/test:test_support",
     "//testing/gtest",
   ]
 }
 
 source_set("snapshots_internal") {
   sources = [
     "snapshot_overlay_provider.h",
     "web_controller_snapshot_helper.h",
     "web_controller_snapshot_helper.mm",
   ]
   deps = [
     ":snapshots",
     "//base",
     "//ios/chrome/browser/tabs",
     "//ios/chrome/browser/ui",
     "//ios/web",
   ]
   libs = [ "UIKit.framework" ]
 }