Use SizesAttributeParser to get the right srcset resource

This CL connects the sizes parser to the extended srcset parser and makes sure the images are properly fetched and displayed.

BUG=357586
Depends on http://crrev.com/242103008

Review URL: https://codereview.chromium.org/236713005

git-svn-id: svn://svn.chromium.org/blink/trunk@172004 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Partial revert of r164563 as those changes have no effect

Revert the changes to HTMLSelectElement.cpp from r164563 as those changes have
no effect and the layout test added in that commit still passes without.

The dragSelection variable is set to true in an "else if" scope. Therefore, it
can never be true when it is evaluated in another "else if" scope below. The
clang static code analyzer was complaining about the dragSelection=true being
a dead assignment.

R=tkent@chromium.org, eseidel@chromium.org
BUG=317809

Review URL: https://codereview.chromium.org/242113014

git-svn-id: svn://svn.chromium.org/blink/trunk@172005 bbb929c8-8fbe-4397-9dbb-9b2b20218538