Add support for caching font files in the Android SkFontMgr.

include/ports/SkFontMgr_android.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkFontMgr_android_DEFINED
 #define SkFontMgr_android_DEFINED
 
@@ skipping 21 matching lines @@
     /** Base path to resolve relative font file names. If a directory, should end with '/'. */
     const char* fBasePath;
 
     /** Optional custom configuration file to use. */
     const char* fFontsXml;
 
     /** Optional custom configuration file for fonts which provide fallback.
      *  In the new style (version > 21) fontsXml format is used, this should be NULL.
      */
     const char* fFallbackFontsXml;
+
+    /** Optional custom flag. If set to true the SkFontMgr will open and cache file streams
+     *  for each font file on initialization.
+     */
+    bool fCacheFontFiles;

[bungeman-skia, 2016/02/08 22:11:56]

I'm not sure I like the naming of this. Perhaps something more like 'fHermetic'
or something, with the comment stating that with this flag set to true, after
the font manager is created it will not attempt to do IO on anything other than
resources/fds it has already acquired. As things stand, the name seems to leak
too much of the implementation as opposed to the intent.

[Khushal, 2016/02/09 00:53:39]

Done.

 };
 
 /** Create a font manager for Android. If 'custom' is NULL, use only system fonts. */
 SK_API SkFontMgr* SkFontMgr_New_Android(const SkFontMgr_Android_CustomFonts* custom);
 
 #endif // SkFontMgr_android_DEFINED