Make "root" flag configurable via CPPLINT.CFG

cpplint.py

@@ -147,6 +147,7 @@
       filter=+filter1,-filter2,...
       exclude_files=regex
       linelength=80
+      root=subdir
 
     "set noparent" option prevents cpplint from traversing directory tree
     upwards looking for more .cfg files in parent directories. This option
@@ -162,6 +163,9 @@
 
     "linelength" allows to specify the allowed line length for the project.
 
+    The "root" option is similar in function to the --root flag (see example
+    above).
+
     CPPLINT.cfg has an effect on files in the same directory and all
     sub-directories, unless overridden by a nested configuration file.
 
@@ -6136,6 +6140,9 @@ def ProcessConfigOverrides(filename):
                 _line_length = int(val)
             except ValueError:
                 sys.stderr.write('Line length must be numeric.')
+          elif name == 'root':
+            global _root
+            _root = val
           else:
             sys.stderr.write(
                 'Invalid configuration option (%s) in file %s\n' %