Adding stack trace to known crashes list.

chrome/test/data/reliability/known_crashes.txt

Index: chrome/test/data/reliability/known_crashes.txt
diff --git a/chrome/test/data/reliability/known_crashes.txt b/chrome/test/data/reliability/known_crashes.txt
index 0c152d38d9cabc970b089f117cbed70c100d6bab..ccaf3ec7a09b12cba052964d5078ba9478f774e2 100644
--- a/chrome/test/data/reliability/known_crashes.txt
+++ b/chrome/test/data/reliability/known_crashes.txt
@@ -187,4 +187,8 @@ webcore::bmpimagereader::decodebmp___webcore::icoimagedecoder::decodeatindex___w
 
 # 47439
 PREFIX:
-webcore::position::getinlineboxandoffset___webcore::position::getinlineboxandoffset___webcore::frame::firstrectforrange___webkit::webviewimpl::caretorselectionbounds
+webcore::position::getinlineboxandoffset___webcore::position::getinlineboxandoffset___webcore::frame::firstrectforrange___webkit::webviewimpl::caretorselectionbounds
+
+# 47839
+PREFIX:
+base::objectwatcher::stopwatching___lockimpl::unlock___`anonymous namespace'::rolloverprotectednow___lockimpl::lock___conditionvariable::signal___watchdog::armsometimedeltaago___`anonymous namespace'::jankobserverhelper::startprocessingtimers___base::messagepumpforio::waitforiocompletion___base::messagepumpforio::dorunloop___base::messagepumpwin::run___messageloop::runinternal___messageloop::run___base::thread::run___base::thread::threadmain___`anonymous namespace'::threadfunc