Bug 1562316 - Fix emoji rendering on android webrender. r=lsalzman

ScaledFontFreeType::GetWRFontInstanceOptions() was neglecting to set
the FontInstanceFlags::EMBEDDED_BITMAPS flag. This was causing us to
always take the non-bitmap path when rasterizing the glyph, which
fails on android because emoji fonts are bitmap only. Setting this
flag causes glyphs to be rendered correctly on android webrender.

Differential Revision: https://phabricator.services.mozilla.com/D40062

gfx/2d/ScaledFontFreeType.cpp

@@ -57,6 +57,7 @@ bool ScaledFontFreeType::GetWRFontInstanceOptions(
   // FIXME: Cairo-FT metrics are not compatible with subpixel positioning.
   // options.flags = wr::FontInstanceFlags_SUBPIXEL_POSITION;
   options.flags = wr::FontInstanceFlags{0};
+  options.flags |= wr::FontInstanceFlags_EMBEDDED_BITMAPS;
   options.bg_color = wr::ToColorU(Color());
   options.synthetic_italics =
       wr::DegreesToSyntheticItalics(GetSyntheticObliqueAngle());