GN: Add logging for the location of an invocation.

tools/gn/input_file_manager.cc

 // Copyright (c) 2013 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.
 
 #include "tools/gn/input_file_manager.h"
 
 #include "base/bind.h"
 #include "base/stl_util.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/parser.h"
@@ skipping 176 matching lines @@
     g_scheduler->FailWithError(err);
 }
 
 bool InputFileManager::LoadFile(const LocationRange& origin,
                                 const BuildSettings* build_settings,
                                 const SourceFile& name,
                                 InputFile* file,
                                 Err* err) {
   // Do all of this stuff outside the lock. We should not give out file
   // pointers until the read is complete.
-  if (g_scheduler->verbose_logging())
-    g_scheduler->Log("Loading", name.value());
+  if (g_scheduler->verbose_logging()) {
+    std::string logmsg = name.value();
+    if (origin.begin().file())
+      logmsg += " (referenced from " + origin.begin().Describe(false) + ")";
+    g_scheduler->Log("Loading", logmsg);
+  }
 
   // Read.
   base::FilePath primary_path = build_settings->GetFullPath(name);
   if (!file->Load(primary_path)) {
     if (!build_settings->secondary_source_path().empty()) {
       // Fall back to secondary source tree.
       base::FilePath secondary_path =
           build_settings->GetFullPathSecondary(name);
       if (!file->Load(secondary_path)) {
         *err = Err(origin, "Can't load input file.",
@@ skipping 47 matching lines @@
     callbacks.swap(data->scheduled_callbacks);
   }
 
   // Run pending invocations. Theoretically we could schedule each of these
   // separately to get some parallelism. But normally there will only be one
   // item in the list, so that's extra overhead and complexity for no gain.
   for (size_t i = 0; i < callbacks.size(); i++)
     callbacks[i].Run(unowned_root);
   return true;
 }