Implemented a policy for centralized setting of the --disk-cache-dir flag.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 9200f857e99205344c2253bc5a45d1c2b766f0ef..fb117869b0106d611793cef9b9e2902f4c5ba6f5 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1282,6 +1282,9 @@ const char kHardwareKeyboardLayout[] = "intl.hardware_keyboard";
 // Whether there is a Flash version installed that supports clearing LSO data.
 const char kClearPluginLSODataEnabled[] = "browser.clear_lso_data_enabled";
 
+// String which specifies where to store the disk cache.
+const char kDiskCacheDir[] = "browser.disk_cache_dir";
+
 // *************** SERVICE PREFS ***************
 // These are attached to the service process.