chrome_paths: refactor and sanitize cache directory handling

base/base_paths.h

Index: base/base_paths.h
diff --git a/base/base_paths.h b/base/base_paths.h
index 0f9be04d0db2aa68f48002629b7d109a7a89e324..7779d9503a4b43285564919fb4eb50d9fee8af78 100644
--- a/base/base_paths.h
+++ b/base/base_paths.h
@@ -32,12 +32,6 @@ enum {
   DIR_SOURCE_ROOT,  // Returns the root of the source tree.  This key is useful
                     // for tests that need to locate various resources.  It
                     // should not be used outside of test code.
-#if defined(OS_POSIX)
-  DIR_USER_CACHE,   // Directory where user cache data resides. The Chromium
-                    // browser cache can be a subdirectory of DIR_USER_CACHE.
-                    // This is $XDG_CACHE_HOME on Linux and ~/Library/Caches
-                    // on Mac.
-#endif
 
   PATH_END
 };