Adding a few more owners to the wasm directory.

Mircea and Andreas have been making changes to wasm.

R=titzer@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2103793006
Cr-Commit-Position: refs/heads/master@{#37401}

src/wasm/OWNERS

 set noparent
 
-titzer@chromium.org
-bradnelson@chromium.org
 ahaas@chromium.org
+bradnelson@chromium.org
+mtrofin@chromium.org
+rossberg@chromium.org
+titzer@chromium.org

test/cctest/wasm/OWNERS

-titzer@chromium.org
-bradnelson@chromium.org
 ahaas@chromium.org
+bradnelson@chromium.org
+mtrofin@chromium.org
+rossberg@chromium.org
+titzer@chromium.org

test/mjsunit/wasm/OWNERS

-titzer@chromium.org
-bradnelson@chromium.org
 ahaas@chromium.org
+bradnelson@chromium.org
+mtrofin@chromium.org
+rossberg@chromium.org
+titzer@chromium.org

test/unittests/wasm/OWNERS

-titzer@chromium.org
-bradnelson@chromium.org
 ahaas@chromium.org
+bradnelson@chromium.org
+mtrofin@chromium.org
+rossberg@chromium.org
+titzer@chromium.org