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..d197bc458f3ab5429aec48cf65d422245b7e79e5 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[];

[gab, 2016/01/21 21:08:49]

kDownloadPreferencePolicyValue to match the pattern of kUpdatePolicyValue?

[Sorin Jianu, 2016/01/25 20:04:58]

Done.

+  static const wchar_t kDownloadPreferenceCacheable[];

[gab, 2016/01/21 21:08:49]

This constant is only ever used in the test?

[Sorin Jianu, 2016/01/25 20:04:58]

The constant is used in the unit test. It had been used in the production code
until we refactored the code to accept a regex. I think it is nice to have it
defined here for documentation purposes but I can move it to the test code as
well.

[gab, 2016/01/25 20:33:50]

I'm not convinced there is a point to document a string which nothing points to
(i.e. unless reading the code from top to bottom no one will ever stumble upon
this...). Plus, as-is there is no comment so it's not really documented either
:-).

I'd say it's best for the API to document how it handles its input (something
that encapsulates this + regex) and then move this to the test (+ comment on
definition in test that it should trigger the documented regex)

   static const int kCheckPeriodOverrideMinutesDefault;
   static const int kCheckPeriodOverrideMinutesMax;
   static const GoogleUpdateSettings::UpdatePolicy kDefaultUpdatePolicy;
@@ -266,6 +270,10 @@ class GoogleUpdateSettings {
   // is assumed not to autoupdate.
   static bool ReenableAutoupdates();
 
+  // Returns a string if the corresponding Google Update group policy is set.
+  // Returns an empty string if no policy or an invalid policy is set.
+  static base::string16 GetDownloadPreference();
+
   // Records UMA stats about Chrome's update policy.
   static void RecordChromeUpdatePolicyHistograms();