feat: enable spare renderer for site per process feature

shell/browser/electron_browser_client.cc

@@ -794,6 +794,26 @@ base::FilePath ElectronBrowserClient::GetLoggingFileName(
   return logging::GetLogFileName(cmd_line);
 }
 
+std::optional<
+    content::ContentBrowserClient::SpareProcessRefusedByEmbedderReason>
+ElectronBrowserClient::ShouldUseSpareRenderProcessHost(
+    content::BrowserContext* browser_context,
+    const GURL& site_url) {
+#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
+  // Extensions should not use a spare process, because they require passing a
+  // command-line flag (switches::kExtensionProcess) to the renderer process
+  // when it launches. A spare process is launched earlier, before it is known
+  // which navigation will use it, so it lacks this flag.
+  if (site_url.SchemeIs(extensions::kExtensionScheme)) {
+    return content::ContentBrowserClient::SpareProcessRefusedByEmbedderReason::
+        ExtensionProcess;
+  }
+  return std::nullopt;
+#else
+  return std::nullopt;
+#endif
+}
+
 std::unique_ptr<net::ClientCertStore>
 ElectronBrowserClient::CreateClientCertStore(
     content::BrowserContext* browser_context) {

shell/browser/electron_browser_client.h

@@ -319,6 +319,10 @@ class ElectronBrowserClient : public content::ContentBrowserClient,
       const blink::StorageKey& storage_key,
       base::OnceCallback<void(bool, const std::string&)> callback) override;
   base::FilePath GetLoggingFileName(const base::CommandLine& cmd_line) override;
+  std::optional<
+      content::ContentBrowserClient::SpareProcessRefusedByEmbedderReason>
+  ShouldUseSpareRenderProcessHost(content::BrowserContext* browser_context,
+                                  const GURL& site_url) override;
 
   // content::RenderProcessHostObserver:
   void RenderProcessHostDestroyed(content::RenderProcessHost* host) override;

shell/browser/feature_list.cc

@@ -45,12 +45,7 @@ void InitializeFeatureList() {
       cmd_line->GetSwitchValueASCII(::switches::kEnableFeatures);
   auto disable_features =
       cmd_line->GetSwitchValueASCII(::switches::kDisableFeatures);
-  // Disable creation of spare renderer process with site-per-process mode,
-  // it interferes with our process preference tracking for non sandboxed mode.
-  // Can be reenabled when our site instance policy is aligned with chromium
-  // when node integration is enabled.
   disable_features +=
-      std::string(",") + features::kSpareRendererForSitePerProcess.name +
       // See https://chromium-review.googlesource.com/c/chromium/src/+/6487926
       // this breaks PDFs locally as we don't have GLIC infra enabled.
       std::string(",") + ax::mojom::features::kScreenAIOCREnabled.name;