Implement `gn analyze`.

tools/gn/gn.gyp

 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
       'target_name': 'gn_lib',
       'type': 'static_library',
       'dependencies': [
         '../../base/base.gyp:base',
@@ skipping 14 matching lines @@
         'builder_record.cc',
         'builder_record.h',
         'bundle_data.cc',
         'bundle_data.h',
         'bundle_data_target_generator.cc',
         'bundle_data_target_generator.h',
         'bundle_file_rule.cc',
         'bundle_file_rule.h',
         'c_include_iterator.cc',
         'c_include_iterator.h',
+        'command_analyze.cc',
         'command_args.cc',
         'command_check.cc',
         'command_clean.cc',
         'command_desc.cc',
         'command_format.cc',
         'command_gen.cc',
         'command_help.cc',
         'command_ls.cc',
         'command_path.cc',
         'command_refs.cc',
@@ skipping 35 matching lines @@
         'function_read_file.cc',
         'function_rebase_path.cc',
         'function_set_default_toolchain.cc',
         'function_set_defaults.cc',
         'function_template.cc',
         'function_toolchain.cc',
         'function_write_file.cc',
         'functions.cc',
         'functions.h',
         'functions_target.cc',
+        'graph.cc',
+        'graph.h',
         'group_target_generator.cc',
         'group_target_generator.h',
         'header_checker.cc',
         'header_checker.h',
         'import_manager.cc',
         'import_manager.h',
         'inherited_libraries.cc',
         'inherited_libraries.h',
         'input_conversion.cc',
         'input_conversion.h',
@@ skipping 154 matching lines @@
         'function_forward_variables_from_unittest.cc',
         'function_get_label_info_unittest.cc',
         'function_get_path_info_unittest.cc',
         'function_get_target_outputs_unittest.cc',
         'function_process_file_template_unittest.cc',
         'function_rebase_path_unittest.cc',
         'function_toolchain_unittest.cc',
         'function_write_file_unittest.cc',
         'functions_target_unittest.cc',
         'functions_unittest.cc',
+        'graph_unittest.cc',
         'header_checker_unittest.cc',
         'inherited_libraries_unittest.cc',
         'input_conversion_unittest.cc',
         'label_pattern_unittest.cc',
         'label_unittest.cc',
         'loader_unittest.cc',
         'ninja_action_target_writer_unittest.cc',
         'ninja_binary_target_writer_unittest.cc',
         'ninja_bundle_data_target_writer_unittest.cc',
         'ninja_copy_target_writer_unittest.cc',
@@ skipping 43 matching lines @@
           'dependencies': [
             'gn_unittests',
           ],
           'includes': [ '../../build/isolate.gypi' ],
           'sources': [ 'gn_unittests.isolate' ],
         },
       ],
     }],
   ],
 }