HTMLPreloadScanner should also add width to non-`w` based image resources

HTMLPreloadScanner should also add width to non-`w` based image resources

The HTMLPreloadScanner was not adding sizes based Width values to
requests issued by <img> tags where only `src` was present or the picked
`srcset` candidate was based on an `x` descriptor.
This CL fixes that issue and adds tests to make sure it won't regress.

BUG=458983
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197640

[Yoav Weiss, 2015-06-22 14:33:07]

yoav@yoav.ws changed reviewers:
+ mkwst@chromium.org

[Yoav Weiss, 2015-06-22 14:33:07]

Hey Mike,

Due to some faulty logic when adding preloadScanner support, I limited precise
"Width:"/"RW" header info only to images resources with a `w` descriptor. This
CL fixes that historical mistake.

Can you take a look? :)

[Mike West, 2015-06-23 09:19:24]

The CQ bit was checked by mkwst@chromium.org

[Mike West, 2015-06-23 09:19:24]

lgtm

[commit-bot: I haz the power, 2015-06-23 09:19:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1196293002/20001

[commit-bot: I haz the power, 2015-06-23 10:26:27]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197640