Move NPObjectBase and PluginChannelBase from content/plugin to content/common

Also rename PluginChannelBase to NPChannelBase, fix variable naming to be agnostic of plugins, and fix a comment in NPChannelBase.

This change is refactoring only and introduces no change in behaviour.

BUG=96703

Review URL: http://codereview.chromium.org/7891003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@101874 0039d316-1c4b-4281-b951-d872f2087c98
18 files changed