Text API does not behave according to specification

1. Make Text.splitText() argument mandatory and stop throwing if the offset is
negative as per the specification:
http://www.w3.org/TR/2012/WD-dom-20121206/#dom-text-splittext

This behavior is consistent with IE10 and Firefox.

2. Make Text.replaceWholeText() argument mandatory as per the DOM3 specification:
http://www.w3.org/TR/DOM-Level-3-Core/core.html#Text3-replaceWholeText

This behavior is consistent with IE10. This function is not supported by Firefox,
likely because it was removed from DOM4.

BUG=267509

Review URL: https://chromiumcodereview.appspot.com/21816003

git-svn-id: svn://svn.chromium.org/blink/trunk@155513 bbb929c8-8fbe-4397-9dbb-9b2b20218538
NodeList.item() does not behave according to specification

NodeList.item() does not behave according to specification:
http://dom.spec.whatwg.org/#nodelist

Namely, we should not throw if the index is negative (meaning we should
drop the [IsIndex] extended attribute) and the argument should be
mandatory.

This behavior is consistent with both IE10 and Firefox.

BUG=237739

Review URL: https://chromiumcodereview.appspot.com/21766002

git-svn-id: svn://svn.chromium.org/blink/trunk@155514 bbb929c8-8fbe-4397-9dbb-9b2b20218538
HTMLSelectElement.item() does not behave according to specification

HTMLSelectElement.item() does not behave according to specification:
http://www.w3.org/TR/html51/forms.html#dom-select-item
http://dom.spec.whatwg.org/#dom-htmlcollection-item

Namely, we should not throw if the offset argument is negative. Also,
the argument should be mandatory.

IE10 and Firefox do not throw when HTMLSelectElement.item() is called
with a negative value (as per the specification).

The argument is mandatory in Firefox but optional in IE10 (it returns
null when called without argument). This looks like a bug in IE because
other item() getters' argument is usually mandatory in IE (e.g.
NodeList.item()).

BUG=237739

Review URL: https://chromiumcodereview.appspot.com/21834002

git-svn-id: svn://svn.chromium.org/blink/trunk@155515 bbb929c8-8fbe-4397-9dbb-9b2b20218538
CharacterData.substringData() arguments should be mandatory

CharacterData.substringData() arguments should be mandatory as per the
specification:
http://dom.spec.whatwg.org/#dom-characterdata-substringdata

Also, we should not throw if the second argument (count) is negative.

This behavior is consistent with IE10 and Firefox.

BUG=237739

Review URL: https://chromiumcodereview.appspot.com/21675003

git-svn-id: svn://svn.chromium.org/blink/trunk@155516 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Support read-only attributes in code generator in python

This is one of migrating binding code generator
from perl to python (with jinja template engine).

With this patch, generator in python newly supports
22 IDLs which contains only readonly attribute.

R=haraken@chromium.org
BUG=262365
TEST=no tests. refactoring.

Review URL: https://chromiumcodereview.appspot.com/21784004

git-svn-id: svn://svn.chromium.org/blink/trunk@155517 bbb929c8-8fbe-4397-9dbb-9b2b20218538