Add UMA for hb_face_t instantiation type

third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp

Index: third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
index 0dbb0a8b4f1384cfed17ba02bd14150f651fc3e9..06bd57d7a5814664342a06fb080c5a5832b8a8b7 100644
--- a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
+++ b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
@@ -30,6 +30,7 @@
 
 #include "platform/fonts/shaping/HarfBuzzFace.h"
 
+#include "platform/Histogram.h"
 #include "platform/fonts/FontCache.h"
 #include "platform/fonts/FontPlatformData.h"
 #include "platform/fonts/SimpleFontData.h"
@@ -56,6 +57,12 @@
 
 namespace blink {
 
+enum HarfBuzzFaceInstantiationTypeUMA {

[Mark P, 2016/06/27 21:28:41]

Please put the standard warning here that these values are written to logs and
should not be renumbered or deleted.

Or, why is this an enumerated histogram rather than simply a BooleanHistogram? 
Do you expect to expand it later?

[drott, 2016/06/28 07:38:47]

I was initially considering reporting the different instantiation type on Mac,
but that's unrelated, so I am switching to BooleanSuccess.

+    HarfBuzzFaceInstantiationTypeInplace = 0,
+    HarfBuzzFaceInstantiationTypeTableCopy,
+    MaxHarfBuzzFaceInstantiationType
+};
+
 struct HbFontDeleter {
     void operator()(hb_font_t* font)
     {
@@ -327,6 +334,9 @@ hb_face_t* HarfBuzzFace::createFace()
 #else
     hb_face_t* face = nullptr;
 
+    DEFINE_STATIC_LOCAL(EnumerationHistogram,
+        faceInstantiationHistogram,
+        ("Blink.Fonts.HarfBuzzFaceInstantiationType", MaxHarfBuzzFaceInstantiationType));
     SkTypeface* typeface = m_platformData->typeface();
     int ttcIndex = 0;
     SkStreamAsset* typefaceStream = typeface->openStream(&ttcIndex);
@@ -342,8 +352,12 @@ hb_face_t* HarfBuzzFace::createFace()
     }
 
     // Fallback to table copies if there is no in-memory access.
-    if (!face)
+    if (!face) {
         face = hb_face_create_for_tables(harfBuzzSkiaGetTable, m_platformData->typeface(), 0);
+        faceInstantiationHistogram.count(HarfBuzzFaceInstantiationTypeTableCopy);
+    } else {
+        faceInstantiationHistogram.count(HarfBuzzFaceInstantiationTypeInplace);
+    }
 #endif
     ASSERT(face);
     return face;