Use PreloadCheckGroup in ExtensionInstallChecker. Make RequirementsChecker a PreloadCheck.

chrome/browser/extensions/crx_installer.h

Index: chrome/browser/extensions/crx_installer.h
diff --git a/chrome/browser/extensions/crx_installer.h b/chrome/browser/extensions/crx_installer.h
index ed2055701a5d0677f7b454b7d904e849278a1c12..9db5d3185174108248ccd279acf365cd34cc3fdb 100644
--- a/chrome/browser/extensions/crx_installer.h
+++ b/chrome/browser/extensions/crx_installer.h
@@ -202,7 +202,7 @@ class CrxInstaller : public SandboxedUnpackerClient {
 
   Profile* profile() { return install_checker_.profile(); }
 
-  const Extension* extension() { return install_checker_.extension().get(); }
+  const Extension* extension() { return extension_.get(); }
 
   // The currently installed version of the extension, for updates. Will be
   // invalid if this isn't an update.
@@ -380,6 +380,9 @@ class CrxInstaller : public SandboxedUnpackerClient {
   // temp_dir_, so we don't have to delete it explicitly.
   base::FilePath unpacked_extension_root_;
 
+  // The extension being installed.
+  scoped_refptr<const Extension> extension_;
+
   // True when the CRX being installed was just downloaded.
   // Used to trigger extra checks before installing.
   bool apps_require_extension_mime_type_;