Update DEPS for chromium roll, fix few sky issues

This updates DEPS to match the recent chromium roll and applies the
following changes to sky to accomodate the skia roll:

https://src.chromium.org/viewvc/blink?revision=184191&view=revision
https://src.chromium.org/viewvc/blink?revision=184289&view=revision

as well as adding #include <string> to WTFString.h so it compiles for
translation units that include this without #including <string>
themselves, which currently happens in a number of files in the android
build.

TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/682573003