Report UseCounter metric when observing NotDef glyphs

third_party/WebKit/Source/core/css/CSSFontSelector.cpp

Index: third_party/WebKit/Source/core/css/CSSFontSelector.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSFontSelector.cpp b/third_party/WebKit/Source/core/css/CSSFontSelector.cpp
index 35460d3064f08567e489fac70a2f8187851b6d5c..4ac4e176f996a0c9a9e4e72aa619c6ec6608ef54 100644
--- a/third_party/WebKit/Source/core/css/CSSFontSelector.cpp
+++ b/third_party/WebKit/Source/core/css/CSSFontSelector.cpp
@@ -34,6 +34,7 @@
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
+#include "core/frame/UseCounter.h"
 #include "core/loader/FrameLoader.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/fonts/FontCache.h"
@@ -173,6 +174,11 @@ void CSSFontSelector::UpdateGenericFontFamilySettings(Document& document) {
   FontCacheInvalidated();
 }
 
+void CSSFontSelector::ReportNotDefGlyph() const {
+  DCHECK(document_);
+  UseCounter::Count(document_, UseCounter::kFontShapingNotDefGlyphObserved);
+}
+
 DEFINE_TRACE(CSSFontSelector) {
   visitor->Trace(document_);
   visitor->Trace(font_face_cache_);