Policy: Add ProxyMode and deprecate ProxyServerMode.

tools/grit/grit/format/policy_templates/writers/template_writer.py

Index: tools/grit/grit/format/policy_templates/writers/template_writer.py
diff --git a/tools/grit/grit/format/policy_templates/writers/template_writer.py b/tools/grit/grit/format/policy_templates/writers/template_writer.py
index 8b742d56a686f33b4917301380357a0330391533..6bbd1dcc028020423a1614ea0450b0402a2a0e3b 100644
--- a/tools/grit/grit/format/policy_templates/writers/template_writer.py
+++ b/tools/grit/grit/format/policy_templates/writers/template_writer.py
@@ -33,6 +33,18 @@ class TemplateWriter(object):
     self.config = config
     self.messages = messages
 
+  def IsDeprecatedPolicySupported(self, policy):
+    '''Checks if the given deprecated policy is supported by the writer.
+
+    Args:
+      policy: The dictionary of the policy.
+
+    Returns:
+      True if the writer chooses to include the deprecated 'policy' in its
+      output.
+    '''
+    return False
+
   def IsPolicySupported(self, policy):
     '''Checks if the given policy is supported by the writer.
     In other words, the set of platforms supported by the writer
@@ -45,6 +57,9 @@ class TemplateWriter(object):
     Returns:
       True if the writer chooses to include 'policy' in its output.
     '''
+    if 'deprecated' in policy and policy['deprecated'] is True:
+      return self.IsDeprecatedPolicySupported(policy)
+
     if '*' in self.platforms:
       # Currently chrome_os is only catched here.
       return True