Improve default value handling for SVGSVGElement.width/height

Improve default value handling for SVGSVGElement.width/height

When a length attribute is either removed or set to an invalid value,
it would get set to '0'. It should however be set to the initial value
specified for the attribute (possibly presentation attribute) in
question.

The test svg/custom/disallow-non-lengths-in-attrs.html is tweaked to
accommodate for this.

BUG=604093
Review URL: https://codereview.chromium.org/1901673003

Cr-Commit-Position: refs/heads/master@{#388250}
(cherry picked from commit 6cd726f3f3ed5d5fecfe725bb3c85dc2cac39e85)

Committed: https://chromium.googlesource.com/chromium/src/+/20a1e339aeac762f323b93575c6cbad86f88cfbb

[fs, 2016-04-25 08:31:45]

Description was changed from

==========
Improve default value handling for SVGSVGElement.width/height

When a length attribute is either removed or set to an invalid value,
it would get set to '0'. It should however be set to the initial value
specified for the attribute (possibly presentation attribute) in
question.

The test svg/custom/disallow-non-lengths-in-attrs.html is tweaked to
accommodate for this.

BUG=604093

Review URL: https://codereview.chromium.org/1901673003

Cr-Commit-Position: refs/heads/master@{#388250}
(cherry picked from commit 6cd726f3f3ed5d5fecfe725bb3c85dc2cac39e85)
==========

to

==========
Improve default value handling for SVGSVGElement.width/height

When a length attribute is either removed or set to an invalid value,
it would get set to '0'. It should however be set to the initial value
specified for the attribute (possibly presentation attribute) in
question.

The test svg/custom/disallow-non-lengths-in-attrs.html is tweaked to
accommodate for this.

BUG=604093

Review URL: https://codereview.chromium.org/1901673003

Cr-Commit-Position: refs/heads/master@{#388250}
(cherry picked from commit 6cd726f3f3ed5d5fecfe725bb3c85dc2cac39e85)

Committed:
https://chromium.googlesource.com/chromium/src/+/20a1e339aeac762f323b93575c6c...
==========

[fs, 2016-04-25 08:31:47]

Committed patchset #1 (id:1) manually as
20a1e339aeac762f323b93575c6cbad86f88cfbb.