Support idle time in CPU profiler

Support idle time in CPU profiler

This change provides an API for the embedder to tell CPU profiler if it is idle or busy with some task. This way we can discriminate between idle time and some native code execution. 

BUG=268947
R=alph@chromium.org, yangguo@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=16109

[alph, 2013-08-07 09:51:59]

lgtm

https://codereview.chromium.org/22412003/diff/3001/src/isolate.h
File src/isolate.h (right):

https://codereview.chromium.org/22412003/diff/3001/src/isolate.h#newcode665
src/isolate.h:665: Address js_entry_sp() {
Can't you just use the js_entry_sp_address?

[yurys, 2013-08-07 10:07:32]

https://codereview.chromium.org/22412003/diff/3001/src/isolate.h
File src/isolate.h (right):

https://codereview.chromium.org/22412003/diff/3001/src/isolate.h#newcode665
src/isolate.h:665: Address js_entry_sp() {
On 2013/08/07 09:51:59, alph wrote:
> Can't you just use the js_entry_sp_address?

That would be inconsistent with the accessors above. We should either use only
foo_address for all or use separate accessors for value and address.

[yurys, 2013-08-07 12:21:26]

Yang, can you do OWNER review please?

[Yang, 2013-08-07 16:23:26]

LGTM with comment.

The visualization tool (tools/plot-timer-event) would surely benefit from this
additional piece of information as well. But if you don't want to deal with
that, I can do that later on.

https://codereview.chromium.org/22412003/diff/3001/src/api.cc
File src/api.cc (right):

https://codereview.chromium.org/22412003/diff/3001/src/api.cc#newcode7643
src/api.cc:7643: if (is_idle) {
Could we assert that the current vm state at this point is either IDLE or
EXTERNAL?

[yurys, 2013-08-07 16:55:44]

As for the plotter support: do you mean adding V8.Idle (similar to V8.External
used by the visualization tool to detect external state) event whenever the
state is changed to IDLE via CpuProfiler::SetIdle call?

As far as I can tell the tool doesn't attribute to the "external" time the time
when there is no v8 functions on the call stack (i.e. when v8's state is
EXTERNAL but V8 itself is not executing anything on the main thread). On the
other hand the IDLE state makes sense for that state. Let's address this
separately if we want to.

https://codereview.chromium.org/22412003/diff/3001/src/api.cc
File src/api.cc (right):

https://codereview.chromium.org/22412003/diff/3001/src/api.cc#newcode7643
src/api.cc:7643: if (is_idle) {
On 2013/08/07 16:23:27, Yang wrote:
> Could we assert that the current vm state at this point is either IDLE or
> EXTERNAL?

Done.

[yurys, 2013-08-07 16:59:21]

As far as I can tell the tool doesn't show anything for the time when there are
no V8 functions on the stack but V8 is in its default state which is EXTERNAL.
So to support the idle time in the visualization tool we would need to add
V8.Idle similar to V8.External and fire corresponding timer events in SetIdle,
right? Let's address this in a separate change if we want to.

[yurys, 2013-08-07 17:04:39]

Committed patchset #3 manually as r16109 (presubmit successful).