Check that directory named depot_tools appears to be full checkout

tools/find_depot_tools.py

Index: tools/find_depot_tools.py
diff --git a/tools/find_depot_tools.py b/tools/find_depot_tools.py
index 0fa151b162c8da3f599ff461024f9cc3e46212a2..32c4d19ea0e42f4b64ef0cae0a78fb861ba669b4 100644
--- a/tools/find_depot_tools.py
+++ b/tools/find_depot_tools.py
@@ -10,23 +10,28 @@ imports breakpad.
 import os
 import sys
 
+
+def IsRealDepotTools(path):
+  return os.path.isfile(os.path.join(path, 'breakpad.py'))
+
+
 def add_depot_tools_to_path():
   """Search for depot_tools and add it to sys.path."""
   # First look if depot_tools is already in PYTHONPATH.
   for i in sys.path:
-    if i.rstrip(os.sep).endswith('depot_tools'):
+    if i.rstrip(os.sep).endswith('depot_tools') and IsRealDepotTools(i):
       return i
   # Then look if depot_tools is in PATH, common case.
   for i in os.environ['PATH'].split(os.pathsep):
-    if i.rstrip(os.sep).endswith('depot_tools'):
+    if i.rstrip(os.sep).endswith('depot_tools') and IsRealDepotTools(i):
       sys.path.append(i.rstrip(os.sep))
       return i
   # 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:
-    if os.path.isfile(os.path.join(root_dir, 'depot_tools', 'breakpad.py')):
-      i = os.path.join(root_dir, 'depot_tools')
+    i = os.path.join(root_dir, 'depot_tools')
+    if IsRealDepotTools(i):
       sys.path.append(i)
       return i
     previous_dir = root_dir