Allow GN imports to be processed from imports.

tools/gn/scope.cc

 // Copyright (c) 2013 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/scope.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "tools/gn/parse_tree.h"
 
@@ skipping 162 matching lines @@
   for (RecordMap::const_iterator i = values_.begin(); i != values_.end(); ++i)
     (*output)[i->first] = i->second.value;
 }
 
 bool Scope::NonRecursiveMergeTo(Scope* dest,
                                 const ParseNode* node_for_err,
                                 const char* desc_for_err,
                                 Err* err) const {
   // Values.
   for (RecordMap::const_iterator i = values_.begin(); i != values_.end(); ++i) {
+    const Value& new_value = i->second.value;
     const Value* existing_value = dest->GetValue(i->first);
-    if (existing_value) {
+    if (existing_value && new_value != *existing_value) {
       // Value present in both the source and the dest.
       std::string desc_string(desc_for_err);
       *err = Err(node_for_err, "Value collision.",
           "This " + desc_string + " contains \"" + i->first.as_string() + "\"");
       err->AppendSubErr(Err(i->second.value, "defined here.",
           "Which would clobber the one in your current scope"));
       err->AppendSubErr(Err(*existing_value, "defined here.",
           "Executing " + desc_string + " should not conflict with anything "
-          "in the current\nscope."));
+          "in the current\nscope unless the values are identical."));
       return false;
     }
     dest->values_[i->first] = i->second;
   }
 
   // Target defaults are owning pointers.
   for (NamedScopeMap::const_iterator i = target_defaults_.begin();
        i != target_defaults_.end(); ++i) {
     if (dest->GetTargetDefaults(i->first)) {
       // TODO(brettw) it would be nice to know the origin of a
@@ skipping 146 matching lines @@
 }
 
 void Scope::AddProvider(ProgrammaticProvider* p) {
   programmatic_providers_.insert(p);
 }
 
 void Scope::RemoveProvider(ProgrammaticProvider* p) {
   DCHECK(programmatic_providers_.find(p) != programmatic_providers_.end());
   programmatic_providers_.erase(p);
 }