Add max post-gc heap usage metrics

Add max post-gc heap usage metrics

- Add per heap max usage metrics.
- Add combined heap (max) usage metrics.

Fixes #24483

R=koda@google.com

Committed: https://github.com/dart-lang/sdk/commit/3abd6ad7583fa0e87158fddbdc7668c851874e5f

[Cutch, 2015-10-06 16:46:42]

johnmccutchan@google.com changed reviewers:
+ koda@google.com, rmacnak@google.com

[koda, 2015-10-06 18:09:02]

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/metrics.cc
File runtime/vm/metrics.cc (right):

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/metrics.cc#n...
runtime/vm/metrics.cc:282: isolate()->heap()->UsedInWords(Heap::kOld) *
kWordSize;
May overflow.

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/pages.h
File runtime/vm/pages.h (right):

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/pages.h#newc...
runtime/vm/pages.h:238: void UpdateGlobalMaxUsed();
General design comment: Why does the PageSpace/Scavenger need to know about all
the metrics that involve its usage? It would be nice for Heap to just be able to
push a stream of its usage stats to some common place, which then
filters+funnels those values to whatever metrics need updating.

[koda, 2015-10-06 18:24:03]

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/metrics.cc
File runtime/vm/metrics.cc (right):

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/metrics.cc#n...
runtime/vm/metrics.cc:282: isolate()->heap()->UsedInWords(Heap::kOld) *
kWordSize;
On 2015/10/06 18:09:02, koda wrote:
> May overflow.

Actually, we should simply change the return type of all the public methods
{Heap,PageSpace,Scavenger}::*InWords to int64_t, since none of them should be
hot.

[Cutch, 2015-10-06 20:23:18]

PTAL

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/metrics.cc
File runtime/vm/metrics.cc (right):

https://codereview.chromium.org/1384003004/diff/20001/runtime/vm/metrics.cc#n...
runtime/vm/metrics.cc:282: isolate()->heap()->UsedInWords(Heap::kOld) *
kWordSize;
On 2015/10/06 18:24:03, koda wrote:
> On 2015/10/06 18:09:02, koda wrote:
> > May overflow.
> 
> Actually, we should simply change the return type of all the public methods
> {Heap,PageSpace,Scavenger}::*InWords to int64_t, since none of them should be
> hot.

Done.

[koda, 2015-10-06 21:12:30]

lgtm

[Cutch, 2015-10-07 13:55:04]

Committed patchset #5 (id:80001) manually as
3abd6ad7583fa0e87158fddbdc7668c851874e5f (presubmit successful).