Add a do_not_sync pref to ExtensionPrefs.

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 93659c567c635674b2a4b8258263107ebf49b16f..fe34b2f1ec016ead88a6f14d973d070a1f152de1 100644
--- a/chrome/browser/extensions/crx_installer.h
+++ b/chrome/browser/extensions/crx_installer.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_
 
 #include <string>
+#include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
@@ -196,6 +197,13 @@ class CrxInstaller
       install_flags_ &= ~kInstallFlagIsEphemeral;
   }
 
+  void set_install_flag(int flag, bool val) {
+    if (val)
+      install_flags_ |= flag;
+    else
+      install_flags_ &= ~flag;
+  }
+
   bool did_handle_successfully() const { return did_handle_successfully_; }
 
   Profile* profile() { return installer_.profile(); }