[autotest] WMatrix link on AFE.

RPC get_static_data will get wmatrix_url from config file and send to frontend.
If wmatrix_url is not present or set to empty, the WMatrix link will not show
up on AFE. Otherwise, it will on the top-right corner.

BUG=chromium:391851
TEST=edit config files, ran afe
DEPLOY=afe,apache

Change-Id: I29948ec59d203ac84d60e68d2c5a9b612b9a4cbc
Reviewed-on: https://chromium-review.googlesource.com/206896
Tested-by: Jiaxi Luo <jiaxiluo@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Jiaxi Luo <jiaxiluo@chromium.org>
diff --git a/frontend/afe/rpc_utils.py b/frontend/afe/rpc_utils.py
index 182641b..971706b 100644
--- a/frontend/afe/rpc_utils.py
+++ b/frontend/afe/rpc_utils.py
@@ -9,8 +9,8 @@
 import datetime, os, inspect
 import django.http
 from autotest_lib.frontend.afe import models, model_logic
-from autotest_lib.client.common_lib import priorities
 from autotest_lib.client.common_lib import control_data, error
+from autotest_lib.client.common_lib import global_config, priorities
 from autotest_lib.server.cros import provision
 
 NULL_DATETIME = datetime.datetime.max
@@ -825,4 +825,14 @@
     try:
         return control_file.encode('ascii')
     except UnicodeDecodeError as e:
-        raise error.ControlFileMalformed(str(e))
\ No newline at end of file
+        raise error.ControlFileMalformed(str(e))
+
+
+def get_wmatrix_url():
+    """Get wmatrix url from config file.
+
+    @returns the wmatrix url or an empty string.
+    """
+    return global_config.global_config.get_config_value('AUTOTEST_WEB',
+                                                        'wmatrix_url',
+                                                        default='')
\ No newline at end of file