Return timestamp of the last recorded interval to the caller of HeapProfiler::GetHeapStats

Return timestamp of the last recorded interval to the caller of HeapProfiler::GetHeapStats

Before this patch the embedder could assign timestamp to the last interval after calling GetHeapStats. This would be slightly different from the timstamps assigned by v8 internally and written into heap snapshot. This patch allow to avoid this small discrepancy by returning timestamp along with last heap stats update.

BUG=chromium:467222
LOG=Y

Committed: https://crrev.com/f13d04d28cf1eb8d6783416d8d3a1d71d82df846
Cr-Commit-Position: refs/heads/master@{#27466}

[yurys, 2015-03-25 16:38:24]

yurys@chromium.org changed reviewers:
+ alph@chromium.org, loislo@chromium.org, yangguo@chromium.org

[alph, 2015-03-25 16:48:54]

lgtm

[yurys, 2015-03-25 16:49:49]

I'm going to wait with landing Blink code that uses the new API until Chrome is
branched to avoid possible problems with reverting bad V8 rolls.

[Yang, 2015-03-26 08:16:23]

On 2015/03/25 16:49:49, yurys wrote:
> I'm going to wait with landing Blink code that uses the new API until Chrome
is
> branched to avoid possible problems with reverting bad V8 rolls.

lgtm.

And yes, please make sure not to use this API until Chrome branch.

[yurys, 2015-03-26 08:17:15]

The CQ bit was checked by yurys@chromium.org

[commit-bot: I haz the power, 2015-03-26 08:17:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1037803002/1

[commit-bot: I haz the power, 2015-03-26 08:34:29]

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

[commit-bot: I haz the power, 2015-03-26 08:34:30]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/1555)

[yurys, 2015-03-26 08:35:16]

The CQ bit was checked by yurys@chromium.org

[commit-bot: I haz the power, 2015-03-26 08:35:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1037803002/1

[commit-bot: I haz the power, 2015-03-26 08:49:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-26 08:50:13]

Patchset 1 (id:??) landed as
https://crrev.com/f13d04d28cf1eb8d6783416d8d3a1d71d82df846
Cr-Commit-Position: refs/heads/master@{#27466}