Revert r144460 "Remove the linux-only CR_SOURCE_ROOT environment variable override of base::DIR_SOU…

base/base_paths_posix.cc

 // Copyright (c) 2012 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 "base/base_paths.h"
 
 #include <ostream>
 #include <string>
 
 #include "build/build_config.h"
@@ skipping 56 matching lines @@
       // There is currently no way to get the executable path on OpenBSD
       char *cpath;
       if ((cpath = getenv("CHROME_EXE_PATH")) != NULL)
         *result = FilePath(cpath);
       else
         *result = FilePath("/usr/local/chrome/chrome");
       return true;
 #endif
     }
     case base::DIR_SOURCE_ROOT: {
+      // Allow passing this in the environment, for more flexibility in build
+      // tree configurations (sub-project builds, gyp --output_dir, etc.)
+      scoped_ptr<base::Environment> env(base::Environment::Create());
+      std::string cr_source_root;
+      if (env->GetVar("CR_SOURCE_ROOT", &cr_source_root)) {
+        path = FilePath(cr_source_root);
+        if (file_util::PathExists(path)) {
+          *result = path;
+          return true;
+        } else {
+          DLOG(WARNING) << "CR_SOURCE_ROOT is set, but it appears to not "
+                        << "point to a directory.";
+        }
+      }
       // On POSIX, unit tests execute two levels deep from the source root.
       // For example:  out/{Debug|Release}/net_unittest
       if (PathService::Get(base::DIR_EXE, &path)) {
         *result = path.DirName().DirName();
         return true;
       }
 
       DLOG(ERROR) << "Couldn't find your source root.  "
                   << "Try running from your chromium/src directory.";
       return false;
     }
     case base::DIR_CACHE:
       scoped_ptr<base::Environment> env(base::Environment::Create());
       FilePath cache_dir(base::nix::GetXDGDirectory(env.get(), "XDG_CACHE_HOME",
                                                     ".cache"));
       *result = cache_dir;
       return true;
   }
   return false;
 }
 
 }  // namespace base