Implement Windows GPO support for "dlpref" in component updater.

chrome/installer/util/google_update_settings.h

Index: chrome/installer/util/google_update_settings.h
diff --git a/chrome/installer/util/google_update_settings.h b/chrome/installer/util/google_update_settings.h
index 115941c94d050d9a6b508bb57a1706c8e9b130d3..6042583a5b793ea216dcf74e04aca6beb1ad95de 100644
--- a/chrome/installer/util/google_update_settings.h
+++ b/chrome/installer/util/google_update_settings.h
@@ -26,9 +26,11 @@ class ChannelInfo;
 class InstallationState;
 }
 
-// This class provides accessors to the Google Update 'ClientState' information
-// that recorded when the user downloads the chrome installer. It is
-// google_update.exe responsibility to write the initial values.
+// This class provides accessors to the Google Update group policies and
+// 'ClientState' information. The group policies are set using specific
+// administrative templates. The 'ClientState' information is recorded when the
+// user downloads the Chrome installer. It is google_update.exe responsibility
+// to write the initial values.
 class GoogleUpdateSettings {
  public:
   // Update policy constants defined by Google Update; do not change these.
@@ -44,6 +46,8 @@ class GoogleUpdateSettings {
   static const wchar_t kUpdatePolicyValue[];
   static const wchar_t kUpdateOverrideValuePrefix[];
   static const wchar_t kCheckPeriodOverrideMinutes[];
+  static const wchar_t kDownloadPreference[];
+  static const wchar_t kDownloadPreferenceCacheable[];
   static const int kCheckPeriodOverrideMinutesDefault;
   static const int kCheckPeriodOverrideMinutesMax;
   static const GoogleUpdateSettings::UpdatePolicy kDefaultUpdatePolicy;
@@ -266,6 +270,11 @@ class GoogleUpdateSettings {
   // is assumed not to autoupdate.
   static bool ReenableAutoupdates();
 
+  // Returns "cacheable" if the Google Update group policy to prefer
+  // cacheable payloads is set. Returns an empty string if no policy or
+  // an unrecognized group policy is set.
+  static base::string16 GetDownloadPreference();
+
   // Records UMA stats about Chrome's update policy.
   static void RecordChromeUpdatePolicyHistograms();