Move existing kSitePerProcess checks to a policy-oracle object

content/browser/frame_host/frame_tree_browsertest.cc

Index: content/browser/frame_host/frame_tree_browsertest.cc
diff --git a/content/browser/frame_host/frame_tree_browsertest.cc b/content/browser/frame_host/frame_tree_browsertest.cc
index 8f35488f1ddc153761e0630efc4de72be87c5484..a0450de934bd091aff5a65f218748f08409f998a 100644
--- a/content/browser/frame_host/frame_tree_browsertest.cc
+++ b/content/browser/frame_host/frame_tree_browsertest.cc
@@ -2,14 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "base/command_line.h"
 #include "content/browser/frame_host/frame_tree.h"
 #include "content/browser/frame_host/frame_tree_node.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
-#include "content/public/common/content_switches.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/test/browser_test_utils.h"
 #include "content/public/test/content_browser_test.h"
@@ -319,7 +317,7 @@ class CrossProcessFrameTreeBrowserTest : public ContentBrowserTest {
   CrossProcessFrameTreeBrowserTest() {}
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
-    command_line->AppendSwitch(switches::kSitePerProcess);
+    IsolateAllSitesForTesting(command_line);
   }
 
   void SetUpOnMainThread() override {