Add support for caching font files in the Android SkFontMgr.

include/ports/SkFontMgr_android.h

Index: include/ports/SkFontMgr_android.h
diff --git a/include/ports/SkFontMgr_android.h b/include/ports/SkFontMgr_android.h
index e489b161b2a602629f6f6a17efeb8b1d9492b5ff..b71b681020e1a643805453f25a5a8e39dd0ec588 100644
--- a/include/ports/SkFontMgr_android.h
+++ b/include/ports/SkFontMgr_android.h
@@ -39,6 +39,11 @@ struct SkFontMgr_Android_CustomFonts {
      *  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. */