Improve Blob constructor error messages.

Improve Blob constructor error messages.

Follow current practice of supplying the name of the constructor in
the error message string, along with normalizing formatting and
wording used.

Also took the opportunity of simplifying how toV8Sequence() reports a
type error: a non-sequence argument is now indicated by returning
v8Undefined().

R=ch.dumez@samsung.com
BUG=270033
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=161849

[sof, 2013-11-12 19:49:41]

At your leisure, please take a look.

[Inactive, 2013-11-12 20:03:56]

lgtm

[commit-bot: I haz the power, 2013-11-12 20:06:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sigbjornf@opera.com/68533014/1

[commit-bot: I haz the power, 2013-11-12 21:05:52]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[commit-bot: I haz the power, 2013-11-12 21:28:45]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sigbjornf@opera.com/68533014/1

[commit-bot: I haz the power, 2013-11-12 21:33:05]

Change committed as 161849