Polish the SystemInfoProvider template code and refactor StorageInfoProvider based on it

chrome/browser/extensions/api/system_info_storage/storage_info_provider.h

Index: chrome/browser/extensions/api/system_info_storage/storage_info_provider.h
diff --git a/chrome/browser/extensions/api/system_info_storage/storage_info_provider.h b/chrome/browser/extensions/api/system_info_storage/storage_info_provider.h
index 18f0e6f7da007c331caebf92c55481464f05d9c1..0265ddd0d04031b56caa45818272d3301c66fe62 100644
--- a/chrome/browser/extensions/api/system_info_storage/storage_info_provider.h
+++ b/chrome/browser/extensions/api/system_info_storage/storage_info_provider.h
@@ -4,14 +4,15 @@
 #ifndef CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_STORAGE_STORAGE_INFO_PROVIDER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_STORAGE_STORAGE_INFO_PROVIDER_H_
 
+#include "chrome/browser/extensions/system_info_provider.h"
 #include "chrome/common/extensions/api/experimental_system_info_storage.h"
 
 namespace extensions {
 namespace systeminfo {
 
-// TODO(hmin): Here the storage type is declared as string type due to the IDL
-// doesn't support enum type yet. Once http://crbug.com/141940 is fixed, we
-// could reuse enum values generated by IDL compiler.
+// TODO(hongbo): Here the storage type is declared as string type due to the
+// IDL doesn't support enum type yet. Once http://crbug.com/141940 is fixed,
+// we could reuse enum values generated by IDL compiler.
 
 // Unknown storage type.
 extern const char kStorageTypeUnknown[];
@@ -19,21 +20,22 @@ extern const char kStorageTypeUnknown[];
 extern const char kStorageTypeHardDisk[];
 // Removable storage, e.g. USB device, flash card reader.
 extern const char kStorageTypeRemovable[];
+
 }  // namespace systeminfo
 
-// An interface for retrieving storage information on different platforms.
-class StorageInfoProvider {
+class StorageInfoProvider
+    : public SystemInfoProvider<
+          api::experimental_system_info_storage::StorageInfo> {
  public:
-   // Return a StorageInfoProvider instance. The caller is responsible for
-   // destroying it.
-   static StorageInfoProvider* Create();
+  virtual ~StorageInfoProvider() {}
 
-   virtual ~StorageInfoProvider() {}
+  // Get the single shared instance of StorageInfoProvider.
+  static StorageInfoProvider* Get();
 
-   // Return true if succeed to get storage information. Should be implemented
-   // on different platforms.
-   virtual bool GetStorageInfo(
-       api::experimental_system_info_storage::StorageInfo* info) = 0;
+  // Get the information for the storage unit specified by the |id| parameter,
+  // and output the result to the |info|.
+  virtual bool QueryUnitInfo(const std::string& id,
+      api::experimental_system_info_storage::StorageUnitInfo* info) = 0;
 };
 
 }  // namespace extensions