Add GN variables for controlling header checking.

tools/gn/header_checker_unittest.cc

 // Copyright 2014 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 <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/config.h"
 #include "tools/gn/header_checker.h"
 #include "tools/gn/scheduler.h"
@@ skipping 208 matching lines @@
     b_.set_output_type(Target::GROUP);
     err = Err();
     EXPECT_TRUE(checker->CheckInclude(&a_, input_file, c_public, range, &err));
     EXPECT_FALSE(err.has_error());
 
     b_.set_output_type(Target::UNKNOWN);
     c_.direct_dependent_configs().clear();
   }
 }
 
+// Checks that the allow_circular_includes_from list works.
+TEST_F(HeaderCheckerTest, CheckIncludeAllowCircular) {
+  InputFile input_file(SourceFile("//some_file.cc"));
+  input_file.SetContents(std::string());
+  LocationRange range;  // Dummy value.
+
+  // Add an include file to A.
+  SourceFile a_public("//a_public.h");
+  a_.sources().push_back(a_public);
+
+  scoped_refptr<HeaderChecker> checker(
+      new HeaderChecker(setup_.build_settings(), targets_));
+
+  // A depends on B. So B normally can't include headers from A.
+  Err err;
+  EXPECT_FALSE(checker->CheckInclude(&b_, input_file, a_public, range, &err));
+  EXPECT_TRUE(err.has_error());
+
+  // Add an allow_circular_includes_from on A that lists B.
+  a_.allow_circular_includes_from().insert(b_.label());
+
+  // Now the include from B to A should be allowed.
+  err = Err();
+  EXPECT_TRUE(checker->CheckInclude(&b_, input_file, a_public, range, &err));
+  EXPECT_FALSE(err.has_error());
+}
+
 TEST_F(HeaderCheckerTest, GetDependentConfigChainProblemIndex) {
   // Assume we have a chain A -> B -> C -> D.
   Target target_a(setup_.settings(), Label(SourceDir("//a/"), "a"));
   Target target_b(setup_.settings(), Label(SourceDir("//b/"), "b"));
   Target target_c(setup_.settings(), Label(SourceDir("//c/"), "c"));
   Target target_d(setup_.settings(), Label(SourceDir("//d/"), "d"));
 
   // C is a group, and B forwards deps from C, so A should get configs from D.
   target_a.set_output_type(Target::SOURCE_SET);
   target_b.set_output_type(Target::SOURCE_SET);
@@ skipping 11 matching lines @@
 
   // If C is not a group, it shouldn't work anymore.
   target_c.set_output_type(Target::SOURCE_SET);
   EXPECT_EQ(1u, HeaderChecker::GetDependentConfigChainProblemIndex(chain));
 
   // Or if B stops forwarding from C, it shouldn't work anymore.
   target_c.set_output_type(Target::GROUP);
   target_b.forward_dependent_configs().clear();
   EXPECT_EQ(2u, HeaderChecker::GetDependentConfigChainProblemIndex(chain));
 }