Add support for generating the QtCreator projects from GN.

tools/gn/import_manager.cc

Index: tools/gn/import_manager.cc
diff --git a/tools/gn/import_manager.cc b/tools/gn/import_manager.cc
index a1555b994541f9aa735c4491c3ea13c2227fd761..01c88b5a68c85dd1bce16a19c78d09d9ba6be4e1 100644
--- a/tools/gn/import_manager.cc
+++ b/tools/gn/import_manager.cc
@@ -111,3 +111,11 @@ bool ImportManager::DoImport(const SourceFile& file,
   return import_scope->NonRecursiveMergeTo(scope, options, node_for_err,
                                            "import", err);
 }
+
+std::vector<SourceFile> ImportManager::GetImportedFiles() const {
+  std::vector<SourceFile> imported_files;
+  imported_files.resize(imports_.size());
+  std::transform(imports_.begin(), imports_.end(), imported_files.begin(),
+                 [](const ImportMap::value_type& val) { return val.first; });
+  return imported_files;
+}