Fix a bug in `gn analyze` related to build-only changes.

tools/gn/analyzer_unittest.cc

 // Copyright 2016 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 "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/analyzer.h"
 #include "tools/gn/build_settings.h"
 #include "tools/gn/builder.h"
 #include "tools/gn/loader.h"
 #include "tools/gn/settings.h"
@@ skipping 182 matching lines @@
       "  \"compile_targets\": [],"
       "  \"test_targets\": [ \"//:a\" ]"
       "}",
       "{"
       "\"error\":"
       "\"Input does not have a key named "
       "\\\"additional_compile_targets\\\" with a list value.\","
       "\"invalid_targets\":[]"
       "}");
 }
+
+TEST_F(AnalyzerTest, BuildFilesWereModified) {
+  // This tests that if a build file is modified, we bail out early with
+  // "Found dependency (all)" error since we can't handle changes to
+  // build files yet (crbug.com/555273).
+  RunBasicTest(
+      "{"
+      "  \"files\": [ \"//a.cc\", \"//BUILD.gn\" ],"
+      "  \"additional_compile_targets\": [],"
+      "  \"test_targets\": [ \"//:a\" ]"
+      "}",
+      "{"
+      "\"compile_targets\":[],"
+      "\"status\":\"Found dependency (all)\","
+      "\"test_targets\":[\"//:a\"]"
+      "}");
+}