Move the follwing members from HTMLPlugInImageElement to HTMLPlugInElement.

Move the follwing members from HTMLPlugInImageElement to HTMLPlugInElement.

 - m_shouldPreferPlugInsForImages and shouldPreferPlugInsForImages()
 - isImageType()
 - m_serviceType
 - m_url

This is a part of tasks to merge HTMLPlugInImageELement into HTMLPlugInElement.
Only HTMLPlugInImageElement inherits from HTMLPlugInElement.

BUG=309978
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=160185

[tkent, 2013-10-22 07:30:58]

hayato-san, morrita-san, would you review this please?
This is the first step to support author ShadowRoot for APPLET, EMBED, and
OBJECT elements.

[hayato, 2013-10-22 07:46:24]

lgtm

[commit-bot: I haz the power, 2013-10-22 07:48:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tkent@chromium.org/34623002/1

[commit-bot: I haz the power, 2013-10-22 09:11:01]

Retried try job too often on linux_blink_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_blin...

[commit-bot: I haz the power, 2013-10-22 09:14:15]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tkent@chromium.org/34623002/1

[commit-bot: I haz the power, 2013-10-22 11:19:14]

Change committed as 160185