Update AshmemRegion::highest_allocated_chunk_ when merging free chunks.

Update AshmemRegion::highest_allocated_chunk_ when merging free chunks.

This is a follow up of r254755 that updated the pointer to the chunk with the
highest address in the region when the highest chunk in the region was being
split (during an allocation reusing a free chunk).

While this was enough to fix the bug specified below, it was only partly
addressing the problem since this pointer also needs to be updated when free
chunks are merged. This CL fixes this issue and adds an extra DCHECK() exposing
the problem with the existing unit tests.

BUG=347919
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=255691

[Philippe, 2014-03-05 12:42:46]

https://codereview.chromium.org/183763037/diff/1/base/memory/discardable_memo...
File base/memory/discardable_memory_allocator_android.cc (right):

https://codereview.chromium.org/183763037/diff/1/base/memory/discardable_memo...
base/memory/discardable_memory_allocator_android.cc:161: 
FYI, I'm adding those blank lines to improve readability. It seems that I'm
getting older and need them now :) I originally liked packed code without many
blank lines for its consistency (since the style guide doesn't really say where
blank lines should be added) but I'm now having a hard time reading it without
some extra blank lines.

[pasko, 2014-03-05 13:36:48]

LGTM++

https://codereview.chromium.org/183763037/diff/1/base/memory/discardable_memo...
File base/memory/discardable_memory_allocator_android.cc (right):

https://codereview.chromium.org/183763037/diff/1/base/memory/discardable_memo...
base/memory/discardable_memory_allocator_android.cc:161: 
On 2014/03/05 12:42:46, Philippe wrote:
> FYI, I'm adding those blank lines to improve readability. It seems that I'm
> getting older and need them now :) I originally liked packed code without many
> blank lines for its consistency (since the style guide doesn't really say
where
> blank lines should be added) but I'm now having a hard time reading it without
> some extra blank lines.

:)
do you mean that when I asked for these extra empty lines I exposed my age
somehow?

[Philippe, 2014-03-05 13:39:11]

Thanks Egor!

https://codereview.chromium.org/183763037/diff/1/base/memory/discardable_memo...
File base/memory/discardable_memory_allocator_android.cc (right):

https://codereview.chromium.org/183763037/diff/1/base/memory/discardable_memo...
base/memory/discardable_memory_allocator_android.cc:161: 
On 2014/03/05 13:36:48, pasko wrote:
> On 2014/03/05 12:42:46, Philippe wrote:
> > FYI, I'm adding those blank lines to improve readability. It seems that I'm
> > getting older and need them now :) I originally liked packed code without
many
> > blank lines for its consistency (since the style guide doesn't really say
> where
> > blank lines should be added) but I'm now having a hard time reading it
without
> > some extra blank lines.
> 
> :)
> do you mean that when I asked for these extra empty lines I exposed my age
> somehow?

Ahaha :)

[Philippe, 2014-03-05 14:10:39]

Hi Mark,

I just realized that r254755 wasn't fully addressing the issue (although it was
enough to make the webgl conformance tests pass again) therefore I would like to
land this additional CL as well.

Thanks,
Philippe.

[Philippe, 2014-03-05 15:36:02]

https://codereview.chromium.org/183763037/diff/20001/base/memory/discardable_...
File base/memory/discardable_memory_allocator_android_unittest.cc (left):

https://codereview.chromium.org/183763037/diff/20001/base/memory/discardable_...
base/memory/discardable_memory_allocator_android_unittest.cc:274:
DiscardableMemoryAllocator allocator_(kAllocatorName, 32 * kPageSize);
FYI, I just uploaded a patch set removing this (which was wrongly added in the
previous CL). |allocator_| is provided by the fixture class instead.

[Philippe, 2014-03-07 13:42:21]

Ping Mark :)

[Mark Mentovai, 2014-03-07 16:38:12]

LGTM. Sorry, I must have missed the original review request.

[Philippe, 2014-03-07 16:44:30]

On 2014/03/07 16:38:12, Mark Mentovai wrote:
> LGTM. Sorry, I must have missed the original review request.

Np, thanks!

[Philippe, 2014-03-07 16:44:34]

The CQ bit was checked by pliard@chromium.org

[commit-bot: I haz the power, 2014-03-07 16:46:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/pliard@chromium.org/183763037/20001

[commit-bot: I haz the power, 2014-03-07 19:52:15]

Change committed as 255691