Add the basic code skeleton for system info event router

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 0265ddd0d04031b56caa45818272d3301c66fe62..d74a39ee47ef8e701255abafba7c149cedb0593b 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
@@ -4,6 +4,8 @@
 #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 "base/file_path.h"
+#include "base/system_monitor/system_monitor.h"
 #include "chrome/browser/extensions/system_info_provider.h"
 #include "chrome/common/extensions/api/experimental_system_info_storage.h"
 
@@ -24,18 +26,70 @@ extern const char kStorageTypeRemovable[];
 }  // namespace systeminfo
 
 class StorageInfoProvider
-    : public SystemInfoProvider<
+    : public base::SystemMonitor::DevicesChangedObserver,
+      public SystemInfoProvider<
           api::experimental_system_info_storage::StorageInfo> {
  public:
-  virtual ~StorageInfoProvider() {}
+  class Delegate {
+   public:
+    virtual ~Delegate() {}
+    // Called when the available capacity is changed.
+    // |id|: identifies the storage unit on which the change happened.
+    // |available_capacity|: the available capacity on the storage unit.
+    virtual void OnStorageDeviceAvailableCapacityChanged(const std::string& id,
+        double available_capacity) = 0;
+
+    // Called when a new storage device is attached to the system, e.g.
+    // a USB disk is plugged in.
+    // |id|: The unique identifier for the storage device attached already.
+    // |type|: The string of storage type. See storage_info_provider.h comment.
+    // |capacity|: The total capacity of the storage device can hold.
+    // |available_capacity|: The available capacity left on the storage device.
+    virtual void OnStorageDeviceAdded(const std::string& id,
+                                      const std::string& type,
+                                      double capacity,
+                                      double available_capacity) = 0;
+
+    // Called when a storage device is removed from the system, e.g.
+    // a USB disk is unplugged.
+    // |id|: the identifier of the storage device that has been removed.
+    virtual void OnStorageDeviceRemoved(const std::string& id) = 0;
+  };
+
+  virtual ~StorageInfoProvider();
 
   // Get the single shared instance of StorageInfoProvider.
   static StorageInfoProvider* Get();
 
-  // 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,
+  // Start watching the storage device change events. Return true if it
+  // succeeds to start, otherwise false is returned.
+  virtual bool StartWatching(Delegate* delegate);
+
+  // Stop watching the storage device change events. Return true if it
+  // succeeds to stop, otherwise false is returned.
+  virtual bool StopWatching();
+
+  // Get the information of the storage unit containing |path|, and output the
+  // result to the |info|.
+  virtual bool QueryUnitInfo(const FilePath::StringType& path,
       api::experimental_system_info_storage::StorageUnitInfo* info) = 0;
+
+  // Overriden from base::SystemMonitor::DevicesChangedObserver.
+  virtual void OnMediaDeviceAttached(const std::string& id,
+      const string16& name, const FilePath::StringType& location) OVERRIDE;
+  virtual void OnMediaDeviceDetached(const std::string& id) OVERRIDE;
+
+ protected:
+  StorageInfoProvider();
+
+  // Platform specific implementation for start and stop watching.
+  virtual bool PlatformStartWatching(Delegate* delegate) = 0;
+  virtual bool PlatformStopWatching() = 0;
+
+  Delegate* delegate_;
+
+  // True if it already started watching the storage change events.
+  bool is_watching_;
 };
 
 }  // namespace extensions