Don't create unnecessary OOPIFs for subframe navigations that don't require a dedicated process.

content/browser/frame_host/render_frame_host_manager.cc

 // Copyright 2013 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.
 
 #include "content/browser/frame_host/render_frame_host_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <string>
@@ skipping 1436 matching lines @@
       return SiteInstanceDescriptor(render_frame_host_->GetSiteInstance());
     }
 
     // This is a cross-site subframe of a non-isolated origin, so place this
     // frame in the default subframe site instance.
     return SiteInstanceDescriptor(
         browser_context, dest_url,
         SiteInstanceRelation::RELATED_DEFAULT_SUBFRAME);
   }
 
+  // Keep subframes in the parent's SiteInstance unless a dedicated process is
+  // required for either the parent or the subframe's destination URL.  This
+  // isn't a strict invariant but rather a heuristic to avoid unnecessary
+  // OOPIFs; see https://crbug.com/711006.  Note that this shouldn't apply to
+  // TopDocumentIsolation, so do this after TDI checks above.
+  if (!frame_tree_node_->IsMainFrame()) {
+    RenderFrameHostImpl* parent =
+        frame_tree_node_->parent()->current_frame_host();
+    bool dest_url_requires_dedicated_process =
+        SiteInstanceImpl::DoesSiteRequireDedicatedProcess(browser_context,
+                                                          dest_url);
+    // Web iframes embedded in DevTools extensions should not reuse the parent
+    // SiteInstance, but DevTools extensions are currently kept in the DevTools
+    // SiteInstance, which is not considered to require a dedicated process.
+    // Work around this by also checking whether the parent's URL requires a
+    // dedicated process.
+    // TODO(alexmos, nick): Remove this once https://crbug.com/706169 is fixed.
+    bool parent_url_requires_dedicated_process =
+        SiteInstanceImpl::DoesSiteRequireDedicatedProcess(
+            browser_context, parent->last_successful_url());
+    if (!parent->GetSiteInstance()->RequiresDedicatedProcess() &&
+        !dest_url_requires_dedicated_process &&
+        !parent_url_requires_dedicated_process) {
+      return SiteInstanceDescriptor(parent->GetSiteInstance());
+    }
+  }
+
   // Start the new renderer in a new SiteInstance, but in the current
   // BrowsingInstance.
   return SiteInstanceDescriptor(browser_context, dest_url,
                                 SiteInstanceRelation::RELATED);
 }
 
 bool RenderFrameHostManager::IsRendererTransferNeededForNavigation(
     RenderFrameHostImpl* rfh,
     const GURL& dest_url) {
   // A transfer is not needed if the current SiteInstance doesn't yet have a
@@ skipping 1341 matching lines @@
           delegate_->IsHidden()) {
     if (delegate_->IsHidden()) {
       render_frame_host_->GetView()->Hide();
     } else {
       render_frame_host_->GetView()->Show();
     }
   }
 }
 
 }  // namespace content