Adds a way to specify test data files for unittests.

base/base_paths_mac.mm

Index: base/base_paths_mac.mm
diff --git a/base/base_paths_mac.mm b/base/base_paths_mac.mm
index aed3ea8e3eb787de288e1c702fd120e752be91d8..a029706e671cd07016cbdf2b6741bbb9264a4348 100644
--- a/base/base_paths_mac.mm
+++ b/base/base_paths_mac.mm
@@ -68,6 +68,8 @@ bool PathProviderMac(int key, FilePath* result) {
 
       // Start with the executable's directory.
       *result = result->DirName();
+
+#if !defined(OS_IOS)
       if (base::mac::AmIBundled()) {
         // The bundled app executables (Chromium, TestShell, etc) live five
         // levels down, eg:
@@ -78,6 +80,7 @@ bool PathProviderMac(int key, FilePath* result) {
         // src/xcodebuild/{Debug|Release}/base_unittests
         *result = result->DirName().DirName();
       }
+#endif
       return true;
     }
     default: