Add system trace points for JavaScript VM entry/exit

Add system trace points for JavaScript VM entry/exit
https://bugs.webkit.org/show_bug.cgi?id=165550

Reviewed by Tim Horton.
Source/JavaScriptCore:

Add trace points for entry/exit into/out of the JS VM.

* runtime/VMEntryScope.cpp:
(JSC::VMEntryScope::VMEntryScope):
(JSC::VMEntryScope::~VMEntryScope):

Source/WTF:

Add trace points for entry/exit into/out of the JS VM.

* wtf/SystemTracing.h:

Tools:

Add trace points for entry/exit into/out of the JS VM.

* Tracing/SystemTracePoints.plist:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@209489 268f45cc-cd09-0410-ab3c-d52691b4dbfc