This patch changes editing/pasteboard/drag-and-drop-objectimage-contenteditable.html to verify dropping image served by object not to be happened, because Blink doesn't allow dropping "object" elements since r146264.

Before r146264, dropping elements are parsed by createFragmentFromMarkup() with  DisallowScriptingAndPluginContentIfNeeded and checking UnsafePluginPastingEnabled settings, which default value is true in DRT.

Since r146264, dropping elements are parse with DisallowScriptingAndPluginContent, DisallowScriptingAndPluginContentIfNeeded enum field is removed, and createFragmentFromMarkup() doesn't check UnsafePluginPastingEnabled settings anymore.

Note: IE and FireFox allow to drop object serving image, but the spec doesn't describe this.

BUG=231950

Review URL: https://chromiumcodereview.appspot.com/19084002

git-svn-id: svn://svn.chromium.org/blink/trunk@154254 bbb929c8-8fbe-4397-9dbb-9b2b20218538