Added UMA instrumentation for site-instrumented user timing marks and measures

Source/core/page/PerformanceUserTiming.cpp

Index: Source/core/page/PerformanceUserTiming.cpp
diff --git a/Source/core/page/PerformanceUserTiming.cpp b/Source/core/page/PerformanceUserTiming.cpp
index a365c6ac690a94788184a0d83140b849057172ab..568fa357f521931876d7f9a2e6efbffa3cf33dcf 100644
--- a/Source/core/page/PerformanceUserTiming.cpp
+++ b/Source/core/page/PerformanceUserTiming.cpp
@@ -31,6 +31,7 @@
 #include "core/page/Performance.h"
 #include "core/page/PerformanceMark.h"
 #include "core/page/PerformanceMeasure.h"
+#include "core/platform/HistogramSupport.h"
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
@@ -107,6 +108,7 @@ void UserTiming::mark(const String& markName, ExceptionState& es)
 
     double startTime = m_performance->now();
     insertPerformanceEntry(m_marksMap, PerformanceMark::create(markName, startTime));
+    HistogramSupport::histogramCustomCounts("PLT.UserTiming_Mark", static_cast<int>(startTime), 0, 600000, 100);
 }
 
 void UserTiming::clearMarks(const String& markName)
@@ -154,6 +156,8 @@ void UserTiming::measure(const String& measureName, const String& startMark, con
     }
 
     insertPerformanceEntry(m_measuresMap, PerformanceMeasure::create(measureName, startTime, endTime));
+    if (endTime >= startTime)
+        HistogramSupport::histogramCustomCounts("PLT.UserTiming_MeasureDuration", static_cast<int>(endTime - startTime), 0, 600000, 100);
 }
 
 void UserTiming::clearMeasures(const String& measureName)