Android app compose text very thin with new WebView.
Originally reported against Chromium as https://bugs.chromium.org/p/chromium/issues/detail?id=678546 , unfortunately currently view-able internal only.
Between Chromium 52.0.2718.0 and 52.0.2720.0 https://chromium.googlesource.com/chromium/src/+/f24ce736e38fa9b159d59dab44b7cc2c69a67849 landed in Chromium. This makes Chromium actually use css font-weight for font selection instead of just doing lookup by 'bold' and 'normal' font-weights. This is generally a good thing.
However, when this change landed in the Android WebView it exposed the fact that the Yahoo Mail App in at least the compose window is using a WebView and specifying font-weight 100 for the text. Previous to the above described change this mapped to a 400 weight font, after this change this mapped to an actual 100 weight font. This makes the text fields in the compose window extremely thin.
On high-dpi devices this very thin text just looks very thin, on lower dpi devices the thin text looks quite thin and low contrast due to the stems not entirely covering any pixels. It is recommended to increase the '100' weight request to at least 300, or 400 to match the previous behavior.