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/vdc.cpp b/vdc.cpp
index b63abbb..ee74146 100644
--- a/vdc.cpp
+++ b/vdc.cpp
@@ -122,6 +122,10 @@
         checkStatus(args, vold->shutdown());
     } else if (args[0] == "volume" && args[1] == "reset") {
         checkStatus(args, vold->reset());
+    } else if (args[0] == "volume" && args[1] == "getStorageSize") {
+        int64_t size;
+        checkStatus(args, vold->getStorageSize(&size));
+        LOG(INFO) << size;
     } else if (args[0] == "cryptfs" && args[1] == "bindkeys") {
         bindkeys(args, vold);
     } else if (args[0] == "cryptfs" && args[1] == "mountFstab" && args.size() == 5) {