Implementation of URLLoader using PluginResource/ResourceHost.

Implementation of URLLoader using PluginResource/ResourceHost. 

This doesn't use the resource call/reply infrastructure, but rather pipes WebKit callbacks to the plugin via unsolicited callbacks. This eliminates state tracking in the host which makes things simpler.

This fixes some bugs in Close() as well to fix the below-mentioned bug.

BUG=69457

[brettw, 2012-12-14 05:33:46]

Moved from https://codereview.chromium.org/11416064/

Patch set 1 is the one from the previous issue, patch set 2 is the one with your
comments addressed, so you can diff them to see what changed.

[bbudge, 2012-12-17 21:13:14]

LGTM just nits really

https://codereview.chromium.org/11416363/diff/7001/ppapi/api/ppp_instance.idl
File ppapi/api/ppp_instance.idl (right):

https://codereview.chromium.org/11416363/diff/7001/ppapi/api/ppp_instance.idl...
ppapi/api/ppp_instance.idl:214: * plugins can't register for MIME type
handling), your implementation of
Is this true? I thought an extension could register a NaCl plugin as a MIME type
handler.

https://codereview.chromium.org/11416363/diff/7001/ppapi/proxy/resource_creat...
File ppapi/proxy/resource_creation_proxy.h (right):

https://codereview.chromium.org/11416363/diff/7001/ppapi/proxy/resource_creat...
ppapi/proxy/resource_creation_proxy.h:44: const PPB_FileRef_CreateInfo&
serialized) OVERRIDE;
'serialized' seems like an odd name in the header. Makes more sense in the .cc
file. How about 'create_info'?

https://codereview.chromium.org/11416363/diff/7001/ppapi/proxy/url_loader_res...
File ppapi/proxy/url_loader_resource.h (right):

https://codereview.chromium.org/11416363/diff/7001/ppapi/proxy/url_loader_res...
ppapi/proxy/url_loader_resource.h:32: // response data is the response for the
already-opened connection.
Does a 'Connection' have a response? I thought a connection was just a pair of
IPC senders.

https://codereview.chromium.org/11416363/diff/7001/webkit/plugins/ppapi/plugi...
File webkit/plugins/ppapi/plugin_delegate.h (right):

https://codereview.chromium.org/11416363/diff/7001/webkit/plugins/ppapi/plugi...
webkit/plugins/ppapi/plugin_delegate.h:681: // The loader object should set
itself on the PluginInstance as the
Maybe clearer if you say the delegate should set the document loader on the
PluginInstance?