[Android] Use upstream blink revision for DevTools frontend URL

Upstream CL https://codereview.chromium.org/488733002 makes
chromium's revision check for blink accept git only commit.
The frontend URL for DevTools must use revision number of
upstream blink.

Fix by generating blink upstream version by crosswalk itself
for the purpose to get frontend URL.
[Android] Specify a later SVN revision of blink in DEPS.xwalk

Because of crbug.com/425155, The frontend assets for devtools
are broken in M39 before r184144. Specify the SVN revision in
DEPS.xwalk with '184144'.

TODO(wang16): Revert this in M40 or M39 past Blink r184144.