Refactorise the policy_path_parser framework

chrome/browser/policy/policy_path_parser.h

Index: chrome/browser/policy/policy_path_parser.h
diff --git a/chrome/browser/policy/policy_path_parser.h b/chrome/browser/policy/policy_path_parser.h
index 5bf03452f7f98b9418f56ce6b183387d3cfb261c..c0d4c222ce858598269eafd34276ccf13b26ac68 100644
--- a/chrome/browser/policy/policy_path_parser.h
+++ b/chrome/browser/policy/policy_path_parser.h
@@ -7,12 +7,31 @@
 
 #include <string>
 
+#include "base/bind.h"
 #include "base/files/file_path.h"
 
 namespace policy {
 
 namespace path_parser {
 
+namespace internal {
+
+typedef bool (*GetValueFuncPtr)(base::FilePath::StringType*);
+
+struct VariableNameAndValueCallback {
+  const base::FilePath::CharType* name;
+  const GetValueFuncPtr value_func_ptr;
+};
+
+// Different set of variables are supported in each platform (see below). Hence
+// this table is filled in with different elements in each platform.
+extern const VariableNameAndValueCallback kVariableNameAndValueCallbacks[];
+
+// Since the number of elements in the table could vary for each platform, this
+// variable is used to keep track of it.
+extern const int kNoOfVariables;
+}
+
 // This function is used to expand the variables in policy strings that
 // represent paths. The set of supported variables differs between platforms
 // but generally covers most standard locations that might be needed in the