Allow Scoped Directory Access on whole volume.

There are some scenarios where an app needs access to the whole SD Card,
not subdirectories. For example, user might have a SDCard with
directories like vacation_pictures (instead of Pictures/vacation);
another example is a file management app.

BUG: 27676858
Change-Id: I20ef713de7e4dfa7e2d7d07bab11898af186d673
diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index d929519..d6f1499 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -1922,10 +1922,12 @@
 
     // User granted access to the request folder; action takes an integer
     // representing the folder's index on Environment.STANDARD_DIRECTORIES
+    // (or -2 for root access, or -1 or unknown directory).
     ACTION_SCOPED_DIRECTORY_ACCESS_GRANTED_BY_FOLDER = 326;
 
     // User denied access to the request folder; action takes an integer
     // representing the folder's index on Environment.STANDARD_DIRECTORIES
+    // (or -2 for root access, or -1 or unknown directory).
     ACTION_SCOPED_DIRECTORY_ACCESS_DENIED_BY_FOLDER = 327;
 
     // User granted access to the request folder; action pass package name
@@ -1939,6 +1941,7 @@
     // App requested access to a directory it has already been granted
     // access before; action takes an integer representing the folder's
     // index on Environment.STANDARD_DIRECTORIES
+    // (or -2 for root access, or -1 or unknown directory).
     ACTION_SCOPED_DIRECTORY_ACCESS_ALREADY_GRANTED_BY_FOLDER = 330;
 
     // App requested access to a directory it has already been granted
@@ -1998,6 +2001,7 @@
 
     // User already denied access to the request folder; action takes an integer
     // representing the folder's index on Environment.STANDARD_DIRECTORIES
+    // (or -2 for root access, or -1 or unknown directory).
     ACTION_SCOPED_DIRECTORY_ACCESS_ALREADY_DENIED_BY_FOLDER = 353;
 
     // User already denied access to the request folder; action pass package name
@@ -2006,6 +2010,7 @@
 
     // User denied access to the request folder and checked 'Do not ask again';
     // action takes an integer representing the folder's index on Environment.STANDARD_DIRECTORIES
+    // (or -2 for root access, or -1 or unknown directory).
     ACTION_SCOPED_DIRECTORY_ACCESS_DENIED_AND_PERSIST_BY_FOLDER = 355;
 
     // User denied access to the request folder and checked 'Do not ask again';