Make -webkit-font-kerning actually work.

Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp

Index: Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
diff --git a/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp b/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
index e297fe4e220e688875b5bb8cfee54752ed2e37c0..37b7fda2c7fc4736cef5327475dfd22fadbea233 100644
--- a/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
+++ b/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2012 Google Inc. All rights reserved.
+ * Copyright (C) 2013 BlackBerry Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -508,6 +509,20 @@ void HarfBuzzShaper::setFontFeatures()
         m_features.append(vrt2);
     }
 
+    static const hb_tag_t kernTag = HB_TAG('k', 'e', 'r', 'n');
+    static hb_feature_t kern = { kernTag, 1, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t noKern = { kernTag, 0, 0, static_cast<unsigned>(-1) };
+    switch (description.kerning()) {
+    case FontDescription::NormalKerning:
+        m_features.append(kern);

[behdad_google, 2013/11/15 22:16:37]

No need to explicitly turn on.  Default is turned on.  Adding it pollutes /
disables hb's internal cache.

+        break;
+    case FontDescription::NoneKerning:
+        m_features.append(noKern);
+        break;
+    case FontDescription::AutoKerning:
+        break;
+    }
+
     FontFeatureSettings* settings = description.featureSettings();
     if (!settings)
         return;