gn: Support build directories outside the source tree.

tools/gn/label.cc

Index: tools/gn/label.cc
diff --git a/tools/gn/label.cc b/tools/gn/label.cc
index f672a3a23c2f5265f7b50ee63f44b6a3bc04d8b9..957ffddabe72aae4c9cc7697c4e3867898060afb 100644
--- a/tools/gn/label.cc
+++ b/tools/gn/label.cc
@@ -28,6 +28,7 @@ bool ComputeBuildLocationFromDep(const Value& input_value,
                                  const SourceDir& current_dir,
                                  const base::StringPiece& input,
                                  SourceDir* result,
+                                 const base::FilePath& source_root,
                                  Err* err) {
   // No rule, use the current locaton.
   if (input.empty()) {
@@ -44,7 +45,7 @@ bool ComputeBuildLocationFromDep(const Value& input_value,
     return false;
   }
 
-  *result = current_dir.ResolveRelativeDir(input);
+  *result = current_dir.ResolveRelativeDir(input, source_root);
   return true;
 }
 
@@ -99,6 +100,7 @@ bool Resolve(const SourceDir& current_dir,
              std::string* out_name,
              SourceDir* out_toolchain_dir,
              std::string* out_toolchain_name,
+             const base::FilePath& source_root,
              Err* err) {
   // To workaround the problem that StringPiece operator[] doesn't return a ref.
   const char* input_str = input.data();
@@ -160,7 +162,7 @@ bool Resolve(const SourceDir& current_dir,
   }
 
   if (!ComputeBuildLocationFromDep(original_value, current_dir, location_piece,
-                                   out_dir, err))
+                                   out_dir, source_root, err))
     return false;
 
   if (!ComputeTargetNameFromDep(original_value, *out_dir, name_piece,
@@ -179,7 +181,8 @@ bool Resolve(const SourceDir& current_dir,
     } else {
       return Resolve(current_dir, current_toolchain,
                      original_value, toolchain_piece,
-                     out_toolchain_dir, out_toolchain_name, NULL, NULL, err);
+                     out_toolchain_dir, out_toolchain_name, NULL, NULL,
+                     source_root, err);
     }
   }
   return true;
@@ -212,6 +215,7 @@ Label::~Label() {
 Label Label::Resolve(const SourceDir& current_dir,
                      const Label& current_toolchain,
                      const Value& input,
+                     const base::FilePath& source_root,
                      Err* err) {
   Label ret;
   if (input.type() != Value::STRING) {
@@ -227,7 +231,7 @@ Label Label::Resolve(const SourceDir& current_dir,
   if (!::Resolve(current_dir, current_toolchain, input, input_string,
                  &ret.dir_, &ret.name_,
                  &ret.toolchain_dir_, &ret.toolchain_name_,
-                 err))
+                 source_root, err))
     return Label();
   return ret;
 }