Drive: add a method to clear all local cache.

chrome/browser/chromeos/gdata/gdata_cache.h

Index: chrome/browser/chromeos/gdata/gdata_cache.h
diff --git a/chrome/browser/chromeos/gdata/gdata_cache.h b/chrome/browser/chromeos/gdata/gdata_cache.h
index 125d2ac986057a61d9d6da37a81e8ebebc0caa2b..c9eb8d449ae7550f6c7c71d32de2868a053ba45a 100644
--- a/chrome/browser/chromeos/gdata/gdata_cache.h
+++ b/chrome/browser/chromeos/gdata/gdata_cache.h
@@ -30,9 +30,10 @@ namespace gdata {
 class GDataCacheEntry;
 class GDataCacheMetadata;
 
-// Callback for SetMountedStateOnUIThread.
+// Callback for SetMountedStateOnUIThread and ClearAllOnUIThread.
 typedef base::Callback<void(GDataFileError error,
-                            const FilePath& file_path)> SetMountedStateCallback;
+                            const FilePath& file_path)>
+    ChangeCacheStateCallback;
 
 // Callback for completion of cache operation.
 typedef base::Callback<void(GDataFileError error,
@@ -229,7 +230,7 @@ class GDataCache {
   //       |dest_path| is the mounted path and |source_path| the unmounted path.
   void SetMountedStateOnUIThread(const FilePath& file_path,
                                  bool to_mount,
-                                 const SetMountedStateCallback& callback);
+                                 const ChangeCacheStateCallback& callback);
 
   // Modifies cache state, which involves the following:
   // - moves |source_path| to |dest_path| in persistent dir, where
@@ -263,6 +264,11 @@ class GDataCache {
   void RemoveOnUIThread(const std::string& resource_id,
                         const CacheOperationCallback& callback);
 
+  // Does the following:
+  // - remove all the files in the cache directory.
+  // - re-create the |metadata_| instance.
+  void ClearAllOnUIThread(const ChangeCacheStateCallback& callback);
+
   // Utility method to call Initialize on UI thread.
   void RequestInitializeOnUIThread();
 
@@ -396,6 +402,9 @@ class GDataCache {
   void Remove(const std::string& resource_id,
               GDataFileError* error);
 
+  // Used to implement ClearAllUIThread.
+  void ClearAll(GDataFileError* error);
+
   // Runs callback and notifies the observers when file is pinned.
   void OnPinned(GDataFileError* error,
                 const std::string& resource_id,