webapk: Avoid overwriting default CreationParams

content/public/browser/site_instance.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_H_
 #define CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 122 matching lines @@
   // Returns true if this SiteInstance is used as the default SiteInstance for
   // cross-site subframes. This only returns true if "top document isolation" is
   // used.
   virtual bool IsDefaultSubframeSiteInstance() const = 0;
 
   // Factory method to create a new SiteInstance.  This will create a new
   // new BrowsingInstance, so it should only be used when creating a new tab
   // from scratch (or similar circumstances).
   //
   // The render process host factory may be nullptr.  See SiteInstance
-  // constructor.
+  // constructor.  |child_process_param_id| is an opaque id used passed to
+  // launch child processes.
   static scoped_refptr<SiteInstance> Create(
-      content::BrowserContext* browser_context);
+      content::BrowserContext* browser_context,
+      int child_process_param_id = 0);

[boliu, 2017/02/23 00:51:30]

I was wary to include child_process_launcher here to get the 0. Do you think
that include is fine? Or maybe DEFAULT_PARAM_ID should be declared here? Or
something else?

 
   // Factory method to get the appropriate SiteInstance for the given URL, in
   // a new BrowsingInstance.  Use this instead of Create when you know the URL,
   // since it allows special site grouping rules to be applied (for example,
-  // to group chrome-ui pages into the same instance).
+  // to group chrome-ui pages into the same instance). Note
+  // |child_process_param_id| is not here purely because no caller uses it.
   static scoped_refptr<SiteInstance> CreateForURL(
       content::BrowserContext* browser_context,
       const GURL& url);
 
   // Return whether both URLs are part of the same web site, for the purpose of
   // assigning them to processes accordingly.  The decision is currently based
   // on the registered domain of the URLs (google.com, bbc.co.uk), as well as
   // the scheme (https, http).  This ensures that two pages will be in
   // the same process if they can communicate with other via JavaScript.
   // (e.g., docs.google.com and mail.google.com have DOM access to each other
@@ skipping 11 matching lines @@
  protected:
   friend class base::RefCounted<SiteInstance>;
 
   SiteInstance() {}
   virtual ~SiteInstance() {}
 };
 
 }  // namespace content.
 
 #endif  // CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_H_