Pass size_t to span functions: storage/

In preparation for upgrading various span args from size_t to
StrictNumeric<size_t>, this fixes type mismatches that would cause
compile errors with that change.

Bug: none
Change-Id: Ic76c9975cdb6431d81645e1930e3f1fdd6d6f4f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6020585
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Ayu Ishii <ayui@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1382665}

storage/browser/file_system/obfuscated_file_util_memory_delegate.cc

@@ -508,20 +508,23 @@ int ObfuscatedFileUtilMemoryDelegate::ReadFile(const base::FilePath& path,
   if (!dp || dp->entry->type != Entry::kFile)
     return net::ERR_FILE_NOT_FOUND;
 
-  int64_t remaining = dp->entry->file_content.size() - offset;
-  if (offset < 0)
+  if (offset < 0 || buf_len < 0) {
     return net::ERR_INVALID_ARGUMENT;
+  }
 
   // Seeking past the end of the file is ok, but returns nothing.
   // This matches FileStream::Context behavior.
-  if (remaining < 0)
+  int64_t remaining = dp->entry->file_content.size() - offset;
+  if (remaining < 0) {
     return 0;
+  }
 
   if (buf_len > remaining)
     buf_len = static_cast<int>(remaining);
 
   base::ranges::copy(
-      base::span(dp->entry->file_content).subspan(offset, buf_len),
+      base::span(dp->entry->file_content)
+          .subspan(static_cast<size_t>(offset), static_cast<size_t>(buf_len)),
       buf->data());
 
   return buf_len;