Chrome 25 is adding two new features to prevent silent extension installs. From the Chrome blog post:
Extensions installed by third party programs using external extension
deployment options will be disabled by default. When a third party
program installs an extension, the Chrome menu will be badged, and
users can click through the Chrome menu to see a dialog containing an
option to enable the extension or to remove it from their computer.
In addition, all extensions previously installed using external
deployment options will be automatically disabled. Chrome will show a
one-time prompt to allow the re-enabling of any of the extensions.
I don't know if this will block all search engine hijacks but it will go a long way to stopping a lot of them.