Revert 166088 "Have getElementsByClassName() / getElementsByTagN..."

Broke unit tests that were relying on Web* interfaces.

For example: http://build.chromium.org/p/chromium.webkit/builders/Android%20Tests%20%28dbg%29/builds/17057/steps/chromiumtestshell_instrumentation_tests/logs/stdio

> Have getElementsByClassName() / getElementsByTagName*() return an HTMLCollection
> 
> Have getElementsByClassName() / getElementsByTagName*() return an HTMLCollection
> instead of a NodeList, as per the specification:
> http://dom.spec.whatwg.org/#document
> http://dom.spec.whatwg.org/#element
> 
> This behavior is consistent with Firefox 26 and IE 11.
> 
> R=arv, haraken, tkent
> BUG=235008
> 
> Review URL: https://codereview.chromium.org/143453010

TBR=ch.dumez@samsung.com

Review URL: https://codereview.chromium.org/139203007

git-svn-id: svn://svn.chromium.org/blink/trunk@166141 bbb929c8-8fbe-4397-9dbb-9b2b20218538