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

base/base_paths_posix.cc

Index: base/base_paths_posix.cc
diff --git a/base/base_paths_posix.cc b/base/base_paths_posix.cc
index d8d5ae61b7285ab113eb46718610a25e08773bf7..a1c45a03df1c470bd15a9af31044ac4241780bc4 100644
--- a/base/base_paths_posix.cc
+++ b/base/base_paths_posix.cc
@@ -74,6 +74,20 @@ bool PathProviderPosix(int key, FilePath* result) {
 #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)) {