Add a check to presubmit.py linting python and SCons files for trailing white...

tools/presubmit.py

Index: tools/presubmit.py
===================================================================
--- tools/presubmit.py	(revision 2110)
+++ tools/presubmit.py	(working copy)
@@ -137,7 +137,7 @@
               or (name == 'third_party'))
 
   IGNORE_LINT = ['flag-definitions.h']
-  
+
   def IgnoreFile(self, name):
     return (super(CppLintProcessor, self).IgnoreFile(name)
               or (name in CppLintProcessor.IGNORE_LINT))
@@ -180,10 +180,12 @@
       'libraries.cc', 'libraries-empty.cc', 'jsmin.py', 'regexp-pcre.js']
   IGNORE_TABS = IGNORE_COPYRIGHTS + ['unicode-test.js',
       'html-comments.js']
+  NO_TRAILING_WHITESPACE_EXTENSIONS = ['py', 'SConscript', 'SConstruct']
 
   def ProcessContents(self, name, contents):
     result = True
     base = basename(name)
+    extension = base.split('.').pop()
     if not base in SourceProcessor.IGNORE_TABS:
       if '\t' in contents:
         print "%s contains tabs" % name
@@ -192,6 +194,10 @@
       if not COPYRIGHT_HEADER_PATTERN.search(contents):
         print "%s is missing a correct copyright header." % name
         result = False
+    if extension in SourceProcessor.NO_TRAILING_WHITESPACE_EXTENSIONS:
+      if ' \n' in contents or contents.endswith(' '):
+        print "%s has trailing whitespace." % name
+        result = False
     return result
 
   def ProcessFiles(self, files):