Speed up generateImage by re-using the outline/bitmap that has already been loaded.

src/ports/SkFontHost_FreeType_common.h

Index: src/ports/SkFontHost_FreeType_common.h
diff --git a/src/ports/SkFontHost_FreeType_common.h b/src/ports/SkFontHost_FreeType_common.h
index 0021dfdd80267c1dfb750bf89aeab5f31aab72c9..843b9d65895433f348fef71fb1ccde79ca0d48cc 100644
--- a/src/ports/SkFontHost_FreeType_common.h
+++ b/src/ports/SkFontHost_FreeType_common.h
@@ -40,6 +40,10 @@ protected:
     void generateGlyphImage(FT_Face face, const SkGlyph& glyph);
     void generateGlyphPath(FT_Face face, SkPath* path);
     void emboldenOutline(FT_Face face, FT_Outline* outline);
+    // This function will update FreeType2 glyph slot.
+    // Let the child class to decide when to call embolden,
+    // such that, we can re-use the outline/bitmap that has been already loaded.
+    void emboldenIfNeeded(FT_Face face, FT_GlyphSlot glyph);
 
 private:
     typedef SkScalerContext INHERITED;