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

tools/gn/analyzer.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 "tools/gn/analyzer.h"
 
 #include <algorithm>
 #include <iterator>
 #include <set>
 #include <vector>
@@ skipping 234 matching lines @@
   for (const auto& label : InvalidLabels(inputs.compile_labels))
     invalid_labels.insert(label);
   for (const auto& label : InvalidLabels(inputs.test_labels))
     invalid_labels.insert(label);
   if (!invalid_labels.empty()) {
     outputs.error = "Invalid targets";
     outputs.invalid_labels = invalid_labels;
     return OutputsToJSON(outputs, default_toolchain_, err);
   }
 
-  TargetSet affected_targets = AllAffectedTargets(inputs.source_files);
-  if (affected_targets.empty()) {
-    outputs.status = "No dependency";
-    return OutputsToJSON(outputs, default_toolchain_, err);
-  }
-
-  // TODO: We can do smarter things when we detect changes to build files.
-  // For example, if all of the ninja files are unchanged, we know that we
-  // can ignore changes to these files. Also, for most .gn files, we can
-  // treat a change as simply affecting every target, config, or toolchain
-  // defined in that file.
+  // TODO(crbug.com/555273): We can do smarter things when we detect changes
+  // to build files. For example, if all of the ninja files are unchanged,
+  // we know that we can ignore changes to these files. Also, for most .gn
+  // files, we can treat a change as simply affecting every target, config,
+  // or toolchain defined in that file.
   if (AnyBuildFilesWereModified(inputs.source_files)) {
     outputs.status = "Found dependency (all)";
     outputs.compile_labels = inputs.compile_labels;
     outputs.test_labels = inputs.test_labels;
     return OutputsToJSON(outputs, default_toolchain_, err);
   }
 
+  TargetSet affected_targets = AllAffectedTargets(inputs.source_files);
+  if (affected_targets.empty()) {
+    outputs.status = "No dependency";
+    return OutputsToJSON(outputs, default_toolchain_, err);
+  }
+
   TargetSet compile_targets = TargetsFor(inputs.compile_labels);
   if (inputs.compile_included_all) {
     for (auto& root : roots_)
       compile_targets.insert(root);
   }
   TargetSet filtered_targets = Filter(compile_targets);
   outputs.compile_labels =
       LabelsFor(Intersect(filtered_targets, affected_targets));
 
   TargetSet test_targets = TargetsFor(inputs.test_labels);
@@ skipping 105 matching lines @@
 void Analyzer::AddAllRefsTo(const Target* target, TargetSet* results) const {
   if (results->find(target) != results->end())
     return;  // Already found this target.
   results->insert(target);
 
   auto dep_begin = dep_map_.lower_bound(target);
   auto dep_end = dep_map_.upper_bound(target);
   for (auto cur_dep = dep_begin; cur_dep != dep_end; cur_dep++)
     AddAllRefsTo(cur_dep->second, results);
 }