Update documentation for SkTypeface constructors.

include/ports/SkFontMgr.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkFontMgr_DEFINED
 #define SkFontMgr_DEFINED
 
@@ skipping 25 matching lines @@
 class SK_API SkFontMgr : public SkRefCnt {
 public:
     int countFamilies() const;
     void getFamilyName(int index, SkString* familyName) const;
     SkFontStyleSet* createStyleSet(int index) const;
 
     /**
      *  The caller must call unref() on the returned object.
      *  Never returns NULL; will return an empty set if the name is not found.
      *
+     *  Passing |nullptr| as the parameter will return the default system font.
+     *
      *  It is possible that this will return a style set not accessible from
      *  createStyleSet(int) due to hidden or auto-activated fonts.
      */
     SkFontStyleSet* matchFamily(const char familyName[]) const;
 
     /**
      *  Find the closest matching typeface to the specified familyName and style
      *  and return a ref to it. The caller must call unref() on the returned
      *  object. Will never return NULL, as it will return the default font if
      *  no matching font is found.
      *
+     *  Passing |nullptr| as the parameter for |familyName| will return the
+     *  default system font.
+     *
      *  It is possible that this will return a style set not accessible from
      *  createStyleSet(int) or matchFamily(const char[]) due to hidden or
      *  auto-activated fonts.
      */
     SkTypeface* matchFamilyStyle(const char familyName[], const SkFontStyle&) const;
 
     /**
      *  Use the system fallback to find a typeface for the given character.
      *  Note that bcp47 is a combination of ISO 639, 15924, and 3166-1 codes,
      *  so it is fine to just pass a ISO 639 here.
      *
      *  Will return NULL if no family can be found for the character
      *  in the system fallback.
      *
+     *  Passing |nullptr| as the parameter for |familyName| will return the
+     *  default system font.
+     *
      *  bcp47[0] is the least significant fallback, bcp47[bcp47Count-1] is the
      *  most significant. If no specified bcp47 codes match, any font with the
      *  requested character will be matched.
      */
     SkTypeface* matchFamilyStyleCharacter(const char familyName[], const SkFontStyle&,
                                           const char* bcp47[], int bcp47Count,
                                           SkUnichar character) const;
 
     SkTypeface* matchFaceStyle(const SkTypeface*, const SkFontStyle&) const;
 
@@ skipping 61 matching lines @@
     virtual SkTypeface* onLegacyCreateTypeface(const char familyName[],
                                                unsigned styleBits) const = 0;
 private:
     static SkFontMgr* Factory();    // implemented by porting layer
     friend SkFontMgr* sk_fontmgr_create_default();
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif