chrome_paths: refactor and sanitize cache directory handling

chrome/common/chrome_paths_linux.cc

Index: chrome/common/chrome_paths_linux.cc
diff --git a/chrome/common/chrome_paths_linux.cc b/chrome/common/chrome_paths_linux.cc
index 42c6ae7e03e103cf1088f387a307fe202043a303..a7fdb07913125470c18dbd63cc0d0da14e104f61 100644
--- a/chrome/common/chrome_paths_linux.cc
+++ b/chrome/common/chrome_paths_linux.cc
@@ -6,6 +6,7 @@
 
 #include "base/environment.h"
 #include "base/file_util.h"
+#include "base/path_service.h"
 #include "base/scoped_ptr.h"
 #include "base/nix/xdg_util.h"
 
@@ -28,6 +29,32 @@ bool GetDefaultUserDataDirectory(FilePath* result) {
   return true;
 }
 
+void GetUserCacheDirectory(const FilePath& profile_dir, FilePath* result) {
+  // See http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
+  // for a spec on where cache files go.  Our rule is:
+  // - if the user-data-dir in the standard place,
+  //     use same subdirectory of the cache directory.
+  //     (this maps ~/.config/google-chrome to ~/.cache/google-chrome as well
+  //      as the same thing for ~/.config/chromium)
+  // - otherwise, use the profile dir directly.
+
+  // Default value in cases where any of the following fails.
+  *result = profile_dir;
+
+  scoped_ptr<base::Environment> env(base::Environment::Create());
+
+  FilePath cache_dir;
+  if (!PathService::Get(base::DIR_CACHE, &cache_dir))
+    return;
+  FilePath config_dir(
+      base::nix::GetXDGDirectory(env.get(), "XDG_CONFIG_HOME", ".config"));
+
+  if (!config_dir.AppendRelativePath(profile_dir, &cache_dir))
+    return;
+
+  *result = cache_dir;
+}
+
 bool GetChromeFrameUserDataDirectory(FilePath* result) {
   scoped_ptr<base::Environment> env(base::Environment::Create());
   FilePath config_dir(