Add preprocessor to reloadOptions in chrome.devtools.inspectedWindow.reload().

Add options.preprocessor to ExtensionServer.js and
provide a default empty string value.

Add test case to extensions-reload.html to verify preprocessingScript is
run.

BUG=229971

Review URL: https://chromiumcodereview.appspot.com/13816005

git-svn-id: svn://svn.chromium.org/blink/trunk@154574 bbb929c8-8fbe-4397-9dbb-9b2b20218538