GN: Add logging for the location of an invocation.

tools/gn/gn.gyp

 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
       'target_name': 'gn_lib',
       'type': 'static_library',
       'dependencies': [
         '../../base/base.gyp:base',
@@ skipping 53 matching lines @@
         'input_file_manager.cc',
         'input_file_manager.h',
         'item.cc',
         'item.h',
         'item_node.cc',
         'item_node.h',
         'item_tree.cc',
         'item_tree.h',
         'label.cc',
         'label.h',
+        'location.cc',
         'location.h',
         'ninja_binary_target_writer.cc',
         'ninja_binary_target_writer.h',
         'ninja_build_writer.cc',
         'ninja_build_writer.h',
         'ninja_copy_target_writer.cc',
         'ninja_copy_target_writer.h',
         'ninja_group_target_writer.cc',
         'ninja_group_target_writer.h',
         'ninja_helper.cc',
@@ skipping 106 matching lines @@
       'type': 'executable',
       'sources': [
         'generate_test_gn_data.cc',
       ],
       'dependencies': [
         '../../base/base.gyp:base',
       ],
     }
   ],
 }