Update mini_chromium to 158694255c7a.
Update mini_chromium to 158694255c7a.

This picks up:

158694255c7a win: undef ERROR, causing failing LOGs
3a981db6e6df MSVC: Disable “warning C4702: unreachable code”.
e87cd9d4dff5 Tidy string16.h after
             https://codereview.chromium.org/809563003/

R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/812683002

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