Revert of Oilpan: always shrink tail-allocated backing storage.

Revert of Oilpan: always shrink tail-allocated backing storage. (patchset #2 id:20001 of https://codereview.chromium.org/1393863004/ )

Reason for revert:
Suspect that this change has caused assertion failures on
Oilpan+Windows+Debug bot.

http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Win%20Oilpan%20%28dbg%29/builds/2955
(Builds are purple because they quit early due to
 too many crashes.)

Crash logs look like:
02:49:04.570 1008   ASSERTION FAILED: header->payloadSize() > newSize
02:49:04.570 1008   Backtrace:
02:49:04.570 1008   	blink::NormalPageHeap::shrinkObject [0x084A1504+148]
02:49:04.570 1008   	blink::HeapAllocator::backingShrink [0x0849AE8A+394]
02:49:04.570 1008   	blink::HeapAllocator::shrinkVectorBacking [0x0849B064+20]
02:49:04.570 1008   	WTF::VectorBuffer<blink::Member<blink::Node>,0,blink::HeapAllocator>::shrinkBuffer [0x189E87A6+134]
02:49:04.570 1008   	WTF::Vector<blink::Member<blink::Node>,0,blink::HeapAllocator>::shrinkCapacity [0x189E8BA6+102]
02:49:04.570 1008   	WTF::Vector<blink::Member<blink::Node>,0,blink::HeapAllocator>::shrinkToFit [0x19A6E65F+31]
02:49:04.570 1008   	blink::DistributedNodes::shrinkToFit [0x19A6E686+22]
(snip)

Original issue's description:
> Oilpan: always shrink tail-allocated backing storage.
>
> When shrinking backing storage allocations, some care is taken not to
> introduce excessive fragmentation and/or limit later expansion of the
> same object. That logic does not need to apply if the backing store is
> at the tail of the current heap chunk: unconditionally reset the
> allocation point, if it is.
>
> R=haraken
> BUG=420515
>
> Committed: https://crrev.com/afa3e61596ebb5d648a6e9923de85534926d27fa
> Cr-Commit-Position: refs/heads/master@{#353321}

TBR=oilpan-reviews@chromium.org,haraken@chromium.org,sigbjornf@opera.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=420515
Committed: https://crrev.com/af6c2e38c9f3928c1472c6d070780894f5ed39e7
Cr-Commit-Position: refs/heads/master@{#354243}

[Yuta Kitamura, 2015-10-15 09:54:43]

Created Revert of Oilpan: always shrink tail-allocated backing storage.

[commit-bot: I haz the power, 2015-10-15 09:54:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1395493008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1395493008/1

[commit-bot: I haz the power, 2015-10-15 09:55:37]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-15 09:56:33]

Patchset 1 (id:??) landed as
https://crrev.com/af6c2e38c9f3928c1472c6d070780894f5ed39e7
Cr-Commit-Position: refs/heads/master@{#354243}

[haraken, 2015-10-15 10:27:32]

LGTM, thanks for the revert!

[sof, 2015-10-15 10:47:19]

lgtm, odd assert - newSize equal to the payload size?

[sof, 2015-10-16 07:04:41]

On 2015/10/15 10:47:19, sof wrote:
> lgtm, odd assert - newSize equal to the payload size?

that was it; added the check.

[haraken, 2015-10-16 07:07:38]

On 2015/10/16 07:04:41, sof wrote:
> On 2015/10/15 10:47:19, sof wrote:
> > lgtm, odd assert - newSize equal to the payload size?
> 
> that was it; added the check.

Where is your new CL?