Make get_label_info take into account the toolchain for target_gen_dir

tools/gn/function_get_label_info_unittest.cc

Index: tools/gn/function_get_label_info_unittest.cc
diff --git a/tools/gn/function_get_label_info_unittest.cc b/tools/gn/function_get_label_info_unittest.cc
index ddec8302c9a79ab308e59c025b858303833e55fc..65e46d050e913456a95c32084a69a3e00230f855 100644
--- a/tools/gn/function_get_label_info_unittest.cc
+++ b/tools/gn/function_get_label_info_unittest.cc
@@ -73,14 +73,20 @@ TEST_F(GetLabelInfoTest, RootGenDir) {
 
 TEST_F(GetLabelInfoTest, TargetOutDir) {
   EXPECT_EQ("//out/Debug/obj/src/foo", Call(":name", "target_out_dir"));
-  EXPECT_EQ("//out/Debug", Call(":name", "root_out_dir"));

[brettw, 2016/08/01 21:53:55]

I don't know why this was here, the same thing is tested above.

-
   EXPECT_EQ("//out/Debug/obj/foo",
             Call("//foo:name(//toolchain:default)", "target_out_dir"));
   EXPECT_EQ("//out/Debug/random/obj/foo",
             Call("//foo:name(//toolchain:random)", "target_out_dir"));
 }
 
+TEST_F(GetLabelInfoTest, TargetGenDir) {
+  EXPECT_EQ("//out/Debug/gen/src/foo", Call(":name", "target_gen_dir"));
+  EXPECT_EQ("//out/Debug/gen/foo",
+            Call("//foo:name(//toolchain:default)", "target_gen_dir"));
+  EXPECT_EQ("//out/Debug/random/gen/foo",
+            Call("//foo:name(//toolchain:random)", "target_gen_dir"));

[brettw, 2016/08/01 21:53:55]

This is the test for the actual bug.

+}
+
 TEST_F(GetLabelInfoTest, LabelNoToolchain) {
   EXPECT_EQ("//src/foo:name", Call(":name", "label_no_toolchain"));
   EXPECT_EQ("//src/foo:name",