Propagate the maximum length of the characters buffer to the TextRun, even when we're only processing a substring. eg. in RenderText, when we're measuring: 'len' glyphs starting from 'text()->characters() + start', then there's a remaining length of 'textLength() - start' that we're not processing. When integrating SVG Fonts with the GlyphPage concept this information is needed to properly handle ligatures. Currently this is done by a special floatWidthUsingSVGFont that takes an "int& extraCharsAvailable" parameter. This generalizes the concept.
Created attachment 96852 [details] Patch
Created attachment 96855 [details] Patch v2 Fix win/wx build.
Comment on attachment 96855 [details] Patch v2 LGTM. Please think about renaming m_len to a more meaningful name in a follow up patch. r=me
Landed in r88613.