Reduce size of HTMLCollection / LiveNodeList / ChildNodeList by 1 word

Reduce size of HTMLCollection / LiveNodeList / ChildNodeList by 1 word

Reduce size of HTMLCollection / LiveNodeList / ChildNodeList by 1 word by
updating the bitfield in CollectionIndexCache so that m_cachedNodeIndex and
m_isLengthCacheValid share 32 bits. Otherwise, the compiler was adding padding
bits after m_isLengthCacheValid to get proper memory alignment.

On my 64 bit Linux machine with gcc 4.8, I see the following size changes:
* HTMLCollection: 72 bytes -> 64 bytes
* LiveNodeList: 72 bytes -> 64 bytes
* ChildNodeList: 56 bytes -> 48 bytes

I ran PerformanceTests/Bindings/node-list-access.html performance test and
could not see any performance impact with this CL.

R=esprehn@chromium.org
BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176603

[esprehn, 2014-06-20 08:17:52]

lgtm, seems reasonable.

[Inactive, 2014-06-20 11:50:21]

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

[commit-bot: I haz the power, 2014-06-20 11:50:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/326073003/1

[commit-bot: I haz the power, 2014-06-20 11:54:17]

Change committed as 176603