Refactor: Inject StatisticsProvider as a dependency of DeviceCloudPolicyInitializer.

chromeos/system/statistics_provider.h

Index: chromeos/system/statistics_provider.h
diff --git a/chromeos/system/statistics_provider.h b/chromeos/system/statistics_provider.h
index 62305e8a3ce9e892e16c5491cc0fd1c7bf135b4a..ef20cca487a037dacfcf64d719e517c0eceb5987 100644
--- a/chromeos/system/statistics_provider.h
+++ b/chromeos/system/statistics_provider.h
@@ -41,6 +41,10 @@ CHROMEOS_EXPORT extern const char kFirmwareTypeValueDeveloper[];
 CHROMEOS_EXPORT extern const char kFirmwareTypeValueNonchrome[];
 CHROMEOS_EXPORT extern const char kFirmwareTypeValueNormal[];
 
+// Serial number key (only VPD v2+ devices).  Use GetMachineID() to cover legacy
+// devices.
+CHROMEOS_EXPORT extern const char kSerialNumberKey[];
+
 // HWID key.
 CHROMEOS_EXPORT extern const char kHardwareClassKey[];
 
@@ -103,12 +107,13 @@ class CHROMEOS_EXPORT StatisticsProvider {
   virtual bool GetMachineStatistic(const std::string& name,
                                    std::string* result) = 0;
 
-  // Checks whether a machine statistic is present (without logging a warning).
-  bool HasMachineStatistic(const std::string& name);
-
   // Similar to GetMachineStatistic for boolean flags.
   virtual bool GetMachineFlag(const std::string& name, bool* result) = 0;
 
+  // Returns the machine serial number after examining a set of well-known
+  // keys. In case no serial is found, an empty string is returned.
+  std::string GetMachineID();
+
   // Cancels any pending file operations.
   virtual void Shutdown() = 0;