Update codesearch links

code.google.com redirects no longer work. This CL replaces links in /tools/mb
to source.chromium.org equivalent.
This CL was uploaded by git cl split.

R=machenbach@chromium.org

Change-Id: I61e216806f67737420db18a2a5ab4994919351af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2392762
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804476}

tools/mb/docs/user_guide.md

@@ -224,7 +224,7 @@ to a file called `runtime_deps` in the build directory, and pass that to
 
 Once GN has computed the lists of runtime dependencies, MB will then
 look up the command line for each target (currently this is hard-coded
-in [mb.py](https://code.google.com/p/chromium/codesearch?q=mb.py#chromium/src/tools/mb/mb.py&q=mb.py%20GetIsolateCommand&sq=package:chromium&type=cs)), and write out the
+in [mb.py](https://source.chromium.org/chromium/chromium/src/+/master:tools/mb/mb.py;l=1370)), and write out the
 matching `.isolate` and `.isolated.gen.json` files.
 
 ## The mb_config.pyl config file