Add Render Process for Site Instance Assignment to content API

This CL adds an enum, SiteInstanceProcessAssignment, which
describes all the ways a SiteInstance may be assigned a render
process. This is exposed in the content API to allow embedders to
record this usage.

See design doc in bug and/or chained CL for more info.

Bug: 1129505
Change-Id: I0654d52b4c0fef3830a877fb1c1476dea4ad9361
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417100
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809620}

content/browser/renderer_host/render_process_host_impl.cc

@@ -4473,19 +4473,32 @@ RenderProcessHost* RenderProcessHostImpl::GetProcessHostForSiteInstance(
     render_process_host = GetUnusedProcessHostForServiceWorker(site_instance);
   }
 
+  if (render_process_host) {
+    site_instance->set_process_assignment(
+        SiteInstanceProcessAssignment::REUSED_EXISTING_PROCESS);
+  }
+
   // See if the spare RenderProcessHost can be used.
   auto& spare_process_manager = SpareRenderProcessHostManager::GetInstance();
   bool spare_was_taken = false;
   if (!render_process_host) {
     render_process_host = spare_process_manager.MaybeTakeSpareRenderProcessHost(
         browser_context, site_instance);
-    spare_was_taken = (render_process_host != nullptr);
+    if (render_process_host) {
+      site_instance->set_process_assignment(
+          SiteInstanceProcessAssignment::USED_SPARE_PROCESS);
+      spare_was_taken = true;
+    }
   }
 
   // If not (or if none found), see if we should reuse an existing process.
   if (!render_process_host && ShouldTryToUseExistingProcessHost(
                                   browser_context, site_info.site_url())) {
     render_process_host = GetExistingProcessHost(site_instance);
+    if (render_process_host) {
+      site_instance->set_process_assignment(
+          SiteInstanceProcessAssignment::REUSED_EXISTING_PROCESS);
+    }
   }
 
   // If we found a process to reuse, sanity check that it is suitable for
@@ -4511,6 +4524,9 @@ RenderProcessHost* RenderProcessHostImpl::GetProcessHostForSiteInstance(
     // issues as TestBrowserContext initialization is done on the main thread.
     render_process_host =
         CreateRenderProcessHost(browser_context, site_instance);
+
+    site_instance->set_process_assignment(
+        SiteInstanceProcessAssignment::CREATED_NEW_PROCESS);
   }
 
   // It is important to call PrepareForFutureRequests *after* potentially

content/browser/site_instance_impl.cc

@@ -163,7 +163,8 @@ SiteInstanceImpl::SiteInstanceImpl(BrowsingInstance* browsing_instance)
       has_site_(false),
       process_reuse_policy_(ProcessReusePolicy::DEFAULT),
       is_for_service_worker_(false),
-      is_guest_(false) {
+      is_guest_(false),
+      process_assignment_(SiteInstanceProcessAssignment::UNKNOWN) {
   DCHECK(browsing_instance);
 }
 
@@ -498,8 +499,8 @@ void SiteInstanceImpl::PreventAssociationWithSpareProcess() {
 void SiteInstanceImpl::SetSite(const GURL& url) {
   // TODO(creis): Consider calling ShouldAssignSiteForURL internally, rather
   // than before multiple call sites.  See https://crbug.com/949220.
-  TRACE_EVENT2("navigation", "SiteInstanceImpl::SetSite",
-               "site id", id_, "url", url.possibly_invalid_spec());
+  TRACE_EVENT2("navigation", "SiteInstanceImpl::SetSite", "site id", id_, "url",
+               url.possibly_invalid_spec());
   // A SiteInstance's site should not change.
   // TODO(creis): When following links or script navigations, we can currently
   // render pages from other sites in this SiteInstance.  This will eventually
@@ -580,6 +581,11 @@ void SiteInstanceImpl::ConvertToDefaultOrSetSite(const GURL& url) {
   SetSite(url);
 }
 
+SiteInstanceProcessAssignment
+SiteInstanceImpl::GetLastProcessAssignmentOutcome() {
+  return process_assignment_;
+}
+
 const GURL& SiteInstanceImpl::GetSiteURL() {
   return site_info_.site_url();
 }
@@ -607,8 +613,9 @@ scoped_refptr<SiteInstance> SiteInstanceImpl::GetRelatedSiteInstance(
 }
 
 bool SiteInstanceImpl::IsRelatedSiteInstance(const SiteInstance* instance) {
-  return browsing_instance_.get() == static_cast<const SiteInstanceImpl*>(
-                                         instance)->browsing_instance_.get();
+  return browsing_instance_.get() ==
+         static_cast<const SiteInstanceImpl*>(instance)
+             ->browsing_instance_.get();
 }
 
 size_t SiteInstanceImpl::GetRelatedActiveContentsCount() {

content/browser/site_instance_impl.h

@@ -236,6 +236,13 @@ class CONTENT_EXPORT SiteInstanceImpl final : public SiteInstance,
   bool RequiresDedicatedProcess() override;
   bool IsSameSiteWithURL(const GURL& url) override;
   bool IsGuest() override;
+  SiteInstanceProcessAssignment GetLastProcessAssignmentOutcome() override;
+
+  // This is called every time a renderer process is assigned to a SiteInstance
+  // and is used by the content embedder for collecting metrics.
+  void set_process_assignment(SiteInstanceProcessAssignment assignment) {
+    process_assignment_ = assignment;
+  }
 
   // The policy to apply when selecting a RenderProcessHost for the
   // SiteInstance. If no suitable RenderProcessHost for the SiteInstance exists
@@ -451,8 +458,7 @@ class CONTENT_EXPORT SiteInstanceImpl final : public SiteInstance,
   // hosts.
   // Only public so that we can make a consistent process swap decision in
   // RenderFrameHostManager.
-  static GURL GetEffectiveURL(BrowserContext* browser_context,
-                              const GURL& url);
+  static GURL GetEffectiveURL(BrowserContext* browser_context, const GURL& url);
 
   // Returns true if pages loaded from |site_info| ought to be handled only by a
   // renderer process isolated from other sites. If --site-per-process is used,
@@ -687,6 +693,9 @@ class CONTENT_EXPORT SiteInstanceImpl final : public SiteInstance,
   // TODO(734722): Move this into the SecurityPrincipal once it is available.
   bool is_guest_;
 
+  // How |this| was last assigned to a renderer process.
+  SiteInstanceProcessAssignment process_assignment_;
+
   base::ObserverList<Observer, true>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SiteInstanceImpl);

content/public/browser/BUILD.gn

@@ -341,6 +341,7 @@ source_set("browser_sources") {
     "shared_worker_instance.h",
     "shared_worker_service.h",
     "site_instance.h",
+    "site_instance_process_assignment.h",
     "site_isolation_policy.cc",
     "site_isolation_policy.h",
     "sms_fetcher.h",

content/public/browser/site_instance.h

@@ -10,6 +10,7 @@
 
 #include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
+#include "content/public/browser/site_instance_process_assignment.h"
 #include "url/gurl.h"
 
 namespace content {
@@ -169,6 +170,12 @@ class CONTENT_EXPORT SiteInstance : public base::RefCounted<SiteInstance> {
   // Returns true if this object is used for a <webview> guest.
   virtual bool IsGuest() = 0;
 
+  // Returns how this SiteInstance was assigned to a renderer process the most
+  // recent time that such an assignment was done. This allows the content
+  // embedder to collect metrics on how renderer process starting or reuse
+  // affects performance.
+  virtual SiteInstanceProcessAssignment GetLastProcessAssignmentOutcome() = 0;
+
   // Factory method to create a new SiteInstance.  This will create a new
   // BrowsingInstance, so it should only be used when creating a new tab from
   // scratch (or similar circumstances).

content/public/browser/site_instance_process_assignment.h

+// Copyright (c) 2020 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_PROCESS_ASSIGNMENT_H_
+#define CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_PROCESS_ASSIGNMENT_H_
+
+namespace content {
+
+// This enum describes how a renderer process is assigned to a SiteInstance.
+enum class SiteInstanceProcessAssignment {
+  // No renderer process has been assigned to the SiteInstance yet.
+  UNKNOWN,
+
+  // Reused some pre-existing process.
+  REUSED_EXISTING_PROCESS,
+
+  // Used an existing spare process.
+  USED_SPARE_PROCESS,
+
+  // No renderer could be reused, so a new one was created for the SiteInstance.
+  CREATED_NEW_PROCESS,
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_PROCESS_ASSIGNMENT_H_