Move attributes-related API from UniqueElementData to AttributeCollection

Move attributes-related API from UniqueElementData to AttributeCollection

Move attributes-related API from UniqueElementData to AttributeCollection
for consistency with the "read-only" attributes API. A new
MutableAttributeCollection class is added to provide attribute addition /
removal API. The rest of the API is moved to a AttributeCollectionGeneric
base class so that it can be shared between AttributeCollection and
MutableAttributeCollection without any code duplication.

R=esprehn@chromium.org, adamk@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179421

[Inactive, 2014-07-14 16:54:39]

I have jsut rebased the patch. Ping review?

[Inactive, 2014-07-31 14:48:32]

ping review.

[esprehn, 2014-08-01 13:48:11]

I think adamk@ is the best reviewer here. I'll admit all these templates are
making the code harder and harder to read and maintain, but I guess it cleans up
the API for the callers.

[Inactive, 2014-08-01 13:52:48]

On 2014/08/01 13:48:11, esprehn wrote:
> I think adamk@ is the best reviewer here. I'll admit all these templates are
> making the code harder and harder to read and maintain, but I guess it cleans
up
> the API for the callers.

Yes, I agree that the templates make things a bit more complex. Sadly, I could
not come up with an easier design that would prevent code duplication between
AttributeCollection and MutableAttributeCollection. At least, this design gets
rid of the code duplication and makes the API consistent between readonly /
mutable.

[adamk, 2014-08-01 15:50:13]

lgtm

[Inactive, 2014-08-01 15:59:27]

The CQ bit was checked by ch.dumez@samsung.com

[commit-bot: I haz the power, 2014-08-01 16:00:21]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/354363002/40001

[commit-bot: I haz the power, 2014-08-01 17:12:29]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/1...)

[commit-bot: I haz the power, 2014-08-01 18:21:15]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-01 18:21:16]

Try jobs failed on following builders:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/1...)

[Inactive, 2014-08-01 18:29:21]

The CQ bit was checked by ch.dumez@samsung.com

[commit-bot: I haz the power, 2014-08-01 18:30:25]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/354363002/40001

[commit-bot: I haz the power, 2014-08-01 19:40:23]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/1...)

[commit-bot: I haz the power, 2014-08-01 20:46:36]

Change committed as 179421