Treat empty string DartPackage as no DartPackage specified

mojo/public/tools/bindings/generators/mojom_dart_generator.py

 # Copyright 2014 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.
 
 """Generates dart source files from a mojom.Module."""
 
 import errno
 import os
 import re
 import shutil
@@ skipping 427 matching lines @@
 
 def IsImportedKind(kind):
   return hasattr(kind, 'imported_from') and kind.imported_from
 
 def ParseStringAttribute(attribute):
   assert isinstance(attribute, basestring)
   return attribute
 
 def GetPackage(module):
   if module.attributes and 'DartPackage' in module.attributes:
-    return ParseStringAttribute(module.attributes['DartPackage'])
+    package = ParseStringAttribute(module.attributes['DartPackage'])
+    package = package.strip()
+    if package != '':
+      return package
   # Default package.
   return 'mojom'
 
 def GetImportUri(module):
   package = GetPackage(module);
   elements = module.namespace.split('.')
   elements.append("%s" % module.name)
   return os.path.join(package, *elements)
 
 def RaiseHelper(msg):
@@ skipping 169 matching lines @@
         interface_to_import[name] = each_import["unique_name"] + "." + name
     return interface_to_import
 
   def ImportedFrom(self):
     interface_to_import = {}
     for each_import in self.module.imports:
       for each_interface in each_import["module"].interfaces:
         name = each_interface.name
         interface_to_import[name] = each_import["unique_name"] + "."
     return interface_to_import