Correctly handle updates over attached Attrs involving null values.

Element attributes having a null value are not stored by the ElementData's
attribute collection. When updating an Element-attached Attr with
a new value, which previously was null, correctly handle updates over
null values (before and after.)

R=
BUG=472840

Review URL: https://codereview.chromium.org/1073823002

git-svn-id: svn://svn.chromium.org/blink/trunk@193484 bbb929c8-8fbe-4397-9dbb-9b2b20218538
4 files changed
tree: 691e5415174a8eca02e3ca00d865d5d4141a71b9
  1. third_party/