mojo_run: infer --origin from `MOJO_VERSION` file if present.

mojo/devtools/common/devtoolslib/paths.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Supports inferring locations of files in default checkout layouts.
 
 These functions allow devtools scripts to work out-of-the-box with regular Mojo
 checkouts.
 """
 
@@ skipping 19 matching lines @@
 def find_within_ancestors(target_relpath, start_path=None):
   """Returns the absolute path to |target_relpath| in the lowest ancestor of
   |start_path| that contains it.
   """
   ancestor = find_ancestor_with(target_relpath, start_path)
   if not ancestor:
     return None
   return os.path.join(ancestor, target_relpath)
 
 
-def infer_paths(is_android, is_debug, target_cpu):
+def infer_params(is_android, is_debug, target_cpu):
   """Infers the locations of select build output artifacts in a regular
   Chromium-like checkout. This should grow thinner or disappear as we introduce
   per-repo config files, see https://github.com/domokit/devtools/issues/28.
 
   Returns:
     Defaultdict with the inferred paths.
   """
   build_dir = (('android_' if is_android else '') +
                (target_cpu + '_' if target_cpu else '') +
                ('Debug' if is_debug else 'Release'))
   out_build_dir = os.path.join('out', build_dir)
 
   root_path = find_ancestor_with(out_build_dir)
-  paths = collections.defaultdict(lambda: None)
+  params = collections.defaultdict(lambda: None)
   if not root_path:
-    return paths
+    return params
 
   build_dir_path = os.path.join(root_path, out_build_dir)
-  paths['build_dir_path'] = build_dir_path
+  params['build_dir_path'] = build_dir_path
   if is_android:
-    paths['shell_path'] = os.path.join(build_dir_path, 'apks', 'MojoShell.apk')
-    paths['adb_path'] = os.path.join(root_path, 'third_party', 'android_tools',
+    params['shell_path'] = os.path.join(build_dir_path, 'apks', 'MojoShell.apk')
+    params['adb_path'] = os.path.join(root_path, 'third_party', 'android_tools',
                                 'sdk', 'platform-tools', 'adb')
   else:
-    paths['shell_path'] = os.path.join(build_dir_path, 'mojo_shell')
-  return paths
+    params['shell_path'] = os.path.join(build_dir_path, 'mojo_shell')
+
+  mojo_version_file = find_within_ancestors('MOJO_VERSION')
+  if mojo_version_file:
+    with open(mojo_version_file) as f:
+      params['mojo_version'] = f.read().strip()
+  return params
 
 
 # Based on Chromium //tools/find_depot_tools.py.
 def find_depot_tools():
   """Searches for depot_tools.
 
   Returns:
     Path to the depot_tools checkout present on the machine, None if not found.
   """
   def _is_real_depot_tools(path):
@@ skipping 10 matching lines @@
   # Rare case, it's not even in PATH, look upward up to root.
   root_dir = os.path.dirname(os.path.abspath(__file__))
   previous_dir = os.path.abspath(__file__)
   while root_dir and root_dir != previous_dir:
     i = os.path.join(root_dir, 'depot_tools')
     if _is_real_depot_tools(i):
       return i
     previous_dir = root_dir
     root_dir = os.path.dirname(root_dir)
   return None