script: Don't do anything before the window size comes in.

This fixes the `getBoundingClientRect()` content test.
Fix parsing of the 'content' property.

Conflicts:
	src/components/style/properties.rs.mako
fix try_to_append_line for ImageBox
auto merge of #1463 : ksh8281/servo/img_new_line, r=pcwalton

````
<div>
   test
   <img src="test.jpeg"/>
</div>
````

if reduce window size, img is disapper.
this pr fixes this case.
CSS parsing/selector-matching for pseudo elements
Implement Document::head()

Implementation details according to the specification below:
http://www.whatwg.org/specs/web-apps/current-work/#dom-document-head

This patch is for:
https://github.com/mozilla/servo/issues/1465
auto merge of #1466 : brunoabinader/servo/document-head, r=kmcallister

Implementation details according to the specification below:
http://www.whatwg.org/specs/web-apps/current-work/#dom-document-head

This patch is for:
https://github.com/mozilla/servo/issues/1465

Closes #1465.
Change range to iter() and add comment for FirstLine and FirstLetter
auto merge of #1409 : pcwalton/servo/fix-get-bounding-client-rect, r=jdm

This fixes the `getBoundingClientRect()` content test.

r? @jdm
auto merge of #1464 : parkjaeman/servo/pseudo-element-selectors-matching, r=SimonSapin

CSS parsing and selector matching for pseudo element :before and :after
Remove some trailing whitespace.
Comment out parsing of ::firt-line and ::first-letter, they’re not supported yet.
Make SelectorMap private.
Remove unused PerOriginRules struct.
Move selector matching tests and testing helpers into a #[cfg(test)] module.
Selector mathing: Move the pseudo-elements buckets inside Stylist.

Refactor to have only one Stylist per document.
Simplify tracking of CSS rules source order in selector matching.
Store selectors in Arc early to avoid some copying.
De-duplicate some redundant code with a macro.
auto merge of #1470 : SimonSapin/servo/before-after, r=metajack

No behavior change (hopefully).

a16087d is the core of what I wanted to do, following up on #1464 (cc: @parkjaeman)