Fix for Minikin native crash
Fix for Minikin native crash

The context start offset wasn't being taken into account for
accumulating the advance values, leading in some cases to array index
overflow.

This is a fix for bug 15327918 "SIGSEGV in
android::MinikinFontSkia::GetSkTypeface()"

Change-Id: I9b646785724c9b72d862b822cd84661c106fbe52

Hixie/sky_engine,mikejurka/engine,devoncarew/sky_engine,aam/engine,flutter/engine,flutter/engine,rmacnak-google/engine,devoncarew/engine,devoncarew/engine,jamesr/flutter_engine,rmacnak-google/engine,krisgiesing/sky_engine,Hixie/sky_engine,devoncarew/sky_engine,rmacnak-google/engine,rmacnak-google/engine,Hixie/sky_engine,jamesr/flutter_engine,krisgiesing/sky_engine,aam/engine,flutter/engine,chinmaygarde/flutter_engine,cdotstout/sky_engine,flutter/engine,mikejurka/engine,cdotstout/sky_engine,tvolkert/engine,mikejurka/engine,devoncarew/sky_engine,tvolkert/engine,chinmaygarde/flutter_engine,jamesr/flutter_engine,aam/engine,tvolkert/engine,tvolkert/engine,devoncarew/engine,jason-simmons/sky_engine,krisgiesing/sky_engine,mikejurka/engine,jamesr/sky_engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,Hixie/sky_engine,devoncarew/engine,cdotstout/sky_engine,jason-simmons/sky_engine,chinmaygarde/flutter_engine,jamesr/flutter_engine,devoncarew/engine,devoncarew/sky_engine,flutter/engine,tvolkert/engine,jamesr/flutter_engine,devoncarew/engine,jason-simmons/sky_engine,jason-simmons/sky_engine,jamesr/flutter_engine,chinmaygarde/sky_engine,jamesr/sky_engine,cdotstout/sky_engine,krisgiesing/sky_engine,krisgiesing/sky_engine,devoncarew/sky_engine,chinmaygarde/sky_engine,chinmaygarde/flutter_engine,chinmaygarde/sky_engine,jamesr/sky_engine,devoncarew/sky_engine,jason-simmons/sky_engine,mikejurka/engine,jason-simmons/flutter_engine,jamesr/sky_engine,jamesr/flutter_engine,jason-simmons/flutter_engine,jamesr/sky_engine,chinmaygarde/sky_engine,tvolkert/engine,krisgiesing/sky_engine,cdotstout/sky_engine,jason-simmons/sky_engine,Hixie/sky_engine,Hixie/sky_engine,aam/engine,cdotstout/sky_engine,jason-simmons/flutter_engine,mikejurka/engine,jason-simmons/sky_engine,jason-simmons/flutter_engine,mikejurka/engine,rmacnak-google/engine,tvolkert/engine,aam/engine,cdotstout/sky_engine,jamesr/flutter_engine,Hixie/sky_engine,jamesr/flutter_engine,krisgiesing/sky_engine,rmacnak-google/engine,chinmaygarde/sky_engine,Hixie/sky_engine,flutter/engine,jason-simmons/flutter_engine,devoncarew/sky_engine,chinmaygarde/sky_engine,flutter/engine,mikejurka/engine,aam/engine,aam/engine,jamesr/sky_engine,chinmaygarde/flutter_engine,aam/engine,jason-simmons/flutter_engine,chinmaygarde/sky_engine,rmacnak-google/engine,chinmaygarde/flutter_engine,flutter/engine,jamesr/sky_engine,mikejurka/engine,devoncarew/engine,jason-simmons/flutter_engine