Reduce heavy runtime calls from debug mirrors.

Reduce heavy runtime calls from debug mirrors.

Cache results of some heavy calls into C++.
This alone will boost the speed up to 18% on some real world scenarios.

BUG=chromium:340285
LOG=Y
R=ulan@chromium.org, yangguo@chromium.org, Yang, rossberg, ulan, yurys

Committed: https://code.google.com/p/v8/source/detail?r=19714

[aandrey, 2014-03-04 09:11:44]

ping?

[ulan, 2014-03-04 10:23:14]

Looks good overall, but I am not familiar with debug mirrors. Now that we cache
results, can it happen that this keeps objects alive that would be dead
otherwise, i.e. can this cause a memory leak?

[aandrey, 2014-03-04 10:46:13]

On 2014/03/04 10:23:14, ulan wrote:
> Looks good overall, but I am not familiar with debug mirrors. Now that we
cache
> results, can it happen that this keeps objects alive that would be dead
> otherwise, i.e. can this cause a memory leak?

This is same as if the client code would cache these results on their side.

For example, in DevTools we would hold a funcMirror and a script, and then a
funcMirror.sourceLocation() call would again fetch the script from the V8
runtime.

Once we release the funcMirror - it's available to GC with all its cached
values.

[ulan, 2014-03-04 10:51:25]

thanks, lgtm

[Yang, 2014-03-04 11:14:26]

On 2014/03/04 10:51:25, ulan wrote:
> thanks, lgtm

lgtm.

[yurys, 2014-03-04 12:35:54]

The CQ bit was checked by yurys@chromium.org

[yurys, 2014-03-04 12:35:55]

The CQ bit was unchecked by yurys@chromium.org

[ulan, 2014-03-07 10:25:59]

Committed patchset #1 manually as r19714 (presubmit successful).