StylePropertySerializer::asText should genearete collect string for background property.

StylePropertySerializer::asText cannot treat background shorthand property correctly.

For example, some StylePropertySet created from "background: none;" is given,
StylePropertySerializer::asText generates:
"background-image: none; background-position: initial initial; background-repeat: initial initial;".

However, background-position and background-repeat is implicit initial value. We cannot use "initial".
And we cannot use either "background-position: initial initial" or "background-repeat: initial initial" as
style element's textContent.

BUG=251510
TESTS=fast/css/background-serialize.html

Review URL: https://codereview.chromium.org/16858019

git-svn-id: svn://svn.chromium.org/blink/trunk@168002 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove Perl from run-bindings-tests

Followup to:
IDL compiler: switch build to Python compiler
https://codereview.chromium.org/166333002/

BUG=239771
R=haraken

Review URL: https://codereview.chromium.org/181003006

git-svn-id: svn://svn.chromium.org/blink/trunk@168003 bbb929c8-8fbe-4397-9dbb-9b2b20218538