devserver: Use absolute path for minidump_stackwalk.

BUG=chromium:715634
TEST=Run local devserver, call symbolicate_dump api.

Change-Id: Iae70c238bc1cd45a85904d4940cfcb54ad7e6d7c
Reviewed-on: https://chromium-review.googlesource.com/489123
Commit-Ready: Xixuan Wu <xixuan@chromium.org>
Tested-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@google.com>
diff --git a/devserver.py b/devserver.py
index fc464ca..b923090 100755
--- a/devserver.py
+++ b/devserver.py
@@ -1216,8 +1216,9 @@
 
       symbols_directory = os.path.join(dl.GetBuildDir(), 'debug', 'breakpad')
 
+      # The location of minidump_stackwalk is defined in chromeos-admin.
       stackwalk = subprocess.Popen(
-          ['minidump_stackwalk', local.name, symbols_directory],
+          ['/usr/local/bin/minidump_stackwalk', local.name, symbols_directory],
           stdout=subprocess.PIPE, stderr=subprocess.PIPE)
 
       to_return, error_text = stackwalk.communicate()