[test] Fix android platform on perf runner

For results processor to work, we need to maintain the assumption that the cwd is equal to the currently running benchmark directory.

NOTRY=true
TBR=clemensh@chromium.org

Change-Id: I585c301dea846194652645973470786ad43aa280
Reviewed-on: https://chromium-review.googlesource.com/444784
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43280}

tools/run_perf.py

@@ -790,6 +790,8 @@ class AndroidPlatform(Platform):  # pragma: no cover
     )
 
   def PreTests(self, node, path):
+    if isinstance(node, RunnableConfig):
+      node.ChangeCWD(path)
     suite_dir = os.path.abspath(os.path.dirname(path))
     if node.path:
       bench_rel = os.path.normpath(os.path.join(*node.path))