Disable off-store extension installs by default.

chrome/browser/download/download_crx_util.h

Index: chrome/browser/download/download_crx_util.h
diff --git a/chrome/browser/download/download_crx_util.h b/chrome/browser/download/download_crx_util.h
index 43de912e1b9db1d5b53d3311fcbc7e6469031f8e..17ac104a36fd2cdc3fb01fc435bcbf50abdd853d 100644
--- a/chrome/browser/download/download_crx_util.h
+++ b/chrome/browser/download/download_crx_util.h
@@ -14,6 +14,7 @@
 
 class CrxInstaller;
 class ExtensionInstallUI;
+class ExtensionService;
 class Profile;
 
 namespace content {
@@ -32,7 +33,8 @@ void SetMockInstallUIForTesting(ExtensionInstallUI* mock_ui);
 // Returns true if the specified download_item containing an extension should be
 // automatically installed. This is typically true in the case of webstore
 // installations.
-bool ShouldOpenExtensionDownload(const content::DownloadItem& download_item);
+bool ShouldOpenExtensionDownload(ExtensionService* service,
+                                 const content::DownloadItem& download_item);
 
 // Start installing a downloaded item item as a CRX (extension, theme, app,
 // ...).  The installer does work on the file thread, so the installation