Files.app: Tell users that the remaining space is 0 bytes when Drive usage is over quota.

chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/extensions/file_manager/private_api_file_system.h"
 
 #include <sys/statvfs.h>
 #include <set>
 
 #include "base/memory/weak_ptr.h"
@@ skipping 412 matching lines @@
   }
   return true;
 }
 
 void FileManagerPrivateGetSizeStatsFunction::GetDriveAvailableSpaceCallback(
     drive::FileError error,
     int64 bytes_total,
     int64 bytes_used) {
   if (error == drive::FILE_ERROR_OK) {
     const uint64 bytes_total_unsigned = bytes_total;
-    const uint64 bytes_remaining_unsigned = bytes_total - bytes_used;
+    // bytes_used can be larger than bytes_total (over quota).
+    const uint64 bytes_remaining_unsigned =
+        std::max(bytes_total - bytes_used, int64(0));
     GetSizeStatsCallback(&bytes_total_unsigned,
                          &bytes_remaining_unsigned);
   } else {
     // If stats couldn't be gotten for drive, result should be left undefined.
     SendResponse(true);
   }
 }
 
 void FileManagerPrivateGetSizeStatsFunction::GetSizeStatsCallback(
     const uint64* total_size,
@@ skipping 452 matching lines @@
   return RespondLater();
 }
 
 void FileManagerPrivateSetEntryTagFunction::OnSetEntryPropertyCompleted(
     drive::FileError result) {
   Respond(result == drive::FILE_ERROR_OK ? NoArguments()
                                          : Error("Failed to set a tag."));
 }
 
 }  // namespace extensions