Add vdc volume getStorageSize

StorageStatsManager.getTotalBytes currently takes the size of /data and
rounds up to known probable sizes to guess the size of internal storage.
This is not always correct.

Instead, find the device /data is on and get the size of that device.
This should give a more accurate answer.

Bug: 295358118
Test: vdc volume getStorageSize returns storage size
Change-Id: I907892041b1ce2cd72092a9877ac34c12bf3f254
diff --git a/VolumeManager.h b/VolumeManager.h
index 943a144..2d6b968 100644
--- a/VolumeManager.h
+++ b/VolumeManager.h
@@ -242,4 +242,10 @@
     bool mSecureKeyguardShowing;
 };
 
+namespace android {
+namespace vold {
+android::status_t GetStorageSize(int64_t* storageSize);
+}
+}  // namespace android
+
 #endif