[Android, Tools] Speed up gn_to_cmake.py with caching

build/android/gradle/gn_to_cmake.py

 #!/usr/bin/env python
 # Copyright 2016 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.
 
 """
 Usage: gn_to_cmake.py <json_file_name>
 
 gn gen out/config --ide=json --json-ide-script=../../gn/gn_to_cmake.py
 
@@ skipping 171 matching lines @@
   return CMakeTargetEscape(cmake_target_name)
 
 
 class Project(object):
   def __init__(self, project_json):
     self.targets = project_json['targets']
     build_settings = project_json['build_settings']
     self.root_path = build_settings['root_path']
     self.build_path = posixpath.join(self.root_path,
                                      build_settings['build_dir'][2:])
+    self.object_source_deps = {}
 
   def GetAbsolutePath(self, path):
     if path.startswith("//"):
       return self.root_path + "/" + path[2:]
     else:
       return path
 
   def GetObjectSourceDependencies(self, gn_target_name, object_dependencies):
     """All OBJECT libraries whose sources have not been absorbed."""
+    if gn_target_name in self.object_source_deps:
+      object_dependencies.update(self.object_source_deps[gn_target_name])
+      return
+    target_deps = set()
     dependencies = self.targets[gn_target_name].get('deps', [])
     for dependency in dependencies:
       dependency_type = self.targets[dependency].get('type', None)
       if dependency_type == 'source_set':
-        object_dependencies.add(dependency)
+        target_deps.add(dependency)
       if dependency_type not in gn_target_types_that_absorb_objects:
-        self.GetObjectSourceDependencies(dependency, object_dependencies)
+        self.GetObjectSourceDependencies(dependency, target_deps)
+    self.object_source_deps[gn_target_name] = target_deps
+    object_dependencies.update(target_deps)
 
   def GetObjectLibraryDependencies(self, gn_target_name, object_dependencies):
     """All OBJECT libraries whose libraries have not been absorbed."""
     dependencies = self.targets[gn_target_name].get('deps', [])
     for dependency in dependencies:
       dependency_type = self.targets[dependency].get('type', None)
       if dependency_type == 'source_set':
         object_dependencies.add(dependency)
         self.GetObjectLibraryDependencies(dependency, object_dependencies)
 
@@ skipping 453 matching lines @@
   json_path = sys.argv[1]
   project = None
   with open(json_path, 'r') as json_file:
     project = json.loads(json_file.read())
 
   WriteProject(Project(project))
 
 
 if __name__ == "__main__":
   main()