DevTools: introduce devtools_paths.py to manage paths

The new devtools_paths.py detects whether the frontend code
is hosted in the Chromium repository, in an external repository during
standalone build, or in an external repository during integrated build.

R=aerotwist@chromium.org

Change-Id: I800ab63f985d203359e387f9c81df9270929b437
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1839791
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#703014}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: dd36b0f6b3fdbaa069facb239773596ae816febb
diff --git a/scripts/run_tests.py b/scripts/run_tests.py
index 5289dcd..6f95fb0 100755
--- a/scripts/run_tests.py
+++ b/scripts/run_tests.py
@@ -9,7 +9,7 @@
 import subprocess
 import sys
 
-import local_node
+import devtools_paths
 
 is_cygwin = sys.platform == "cygwin"
 chrome_binary = None
@@ -48,9 +48,9 @@
     karma_errors_found = False
 
     karmaconfig_path = os.path.join(devtools_path, "karma.conf.js")
-    exec_command = [local_node.node_path(), local_node.karma_path(), "start", to_platform_path_exact(karmaconfig_path)]
+    exec_command = [devtools_paths.node_path(), devtools_paths.karma_path(), "start", to_platform_path_exact(karmaconfig_path)]
 
-    env = {'NODE_PATH': local_node.node_modules_path()}
+    env = {'NODE_PATH': devtools_paths.node_modules_path()}
     if (chrome_binary is not None):
         env['CHROME_BIN'] = chrome_binary