Test for generated files being detected during `gn check`.

tools/gn/test_with_scope.cc

Index: tools/gn/test_with_scope.cc
diff --git a/tools/gn/test_with_scope.cc b/tools/gn/test_with_scope.cc
index 896b5792dfe99ec1e57ff3dc4703c8af4f8246e6..626fd928ec45ee2ae76725dd346fb854b051dbf5 100644
--- a/tools/gn/test_with_scope.cc
+++ b/tools/gn/test_with_scope.cc
@@ -8,13 +8,18 @@
 #include "tools/gn/parser.h"
 #include "tools/gn/tokenizer.h"
 
+static BuildSettings BuildSettingsWithBuildDir(const std::string& dir) {
+  BuildSettings build_settings;
+  build_settings.SetBuildDir(SourceDir(dir));
+  return build_settings;
+}
+
 TestWithScope::TestWithScope()
-    : build_settings_(),
+    : build_settings_(BuildSettingsWithBuildDir("//out/Debug/")),

[jbroman, 2015/11/27 19:48:26]

This is somewhat subtle, but the Settings constructor copies the build dir out
of build_settings_ before SetBuildDir is called otherwise, leading to there not
being a generated output dir.

       settings_(&build_settings_, std::string()),
       toolchain_(&settings_, Label(SourceDir("//toolchain/"), "default")),
       scope_(&settings_),
       scope_progammatic_provider_(&scope_, true) {
-  build_settings_.SetBuildDir(SourceDir("//out/Debug/"));
   build_settings_.set_print_callback(
       base::Bind(&TestWithScope::AppendPrintOutput, base::Unretained(this)));