The current shaping implementation in blink computes the bounds for each glyph after shaping, in ShapeResult::ComputeGlyphPositions, by calling SimpleFontData::BoundsForGlyph for each glyph.

This eventually calls into the Skia SkPaint::getTextWidths method.

We spend more time doing glyph computation than shaping in many cases, even though shaping also needs the text metrics. 

Ideally we'd get the bounds as a part of the shaping operation but that's a big change. Another option would be to call SkPaint::getTextWidths for the entire glyph buffer at once (as it takes a list of glyphs) instead of doing it per glyph.

This isn't urgent at all but might be an interesting optimization opportunity in the future.