[Nearby] Correctly implement InputFile::Read().

The prior implementation of this function assumed that the provided
|size| would match the number of bytes read. In reality, |size| is
generally a very large value and number of bytes read may be smaller
than it.

Manually verified by successfully sending a 7KB file from Chrome OS
to Android.

Bug: 1124992
Change-Id: I781a2c1f69aee374a18c10641ed14f31eb7348f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2393616Reviewed-by: James Vecore <vecore@google.com>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805409}

chrome/services/sharing/nearby/platform_v2/input_file.cc

@@ -30,12 +30,13 @@ ExceptionOr<ByteArray> InputFile::Read(std::int64_t size) {
   if (!file_.IsValid())
     return Exception::kIo;
 
-  ByteArray bytes(size);
-  int bytes_read = file_.ReadAtCurrentPos(bytes.data(), bytes.size());
-  if (bytes_read != size)
+  char buf[size];
+  int num_bytes_read = file_.ReadAtCurrentPos(buf, size);
+
+  if (num_bytes_read < 0 || num_bytes_read > GetTotalSize())
     return Exception::kIo;
 
-  return ExceptionOr<ByteArray>(std::move(bytes));
+  return ExceptionOr<ByteArray>(ByteArray(buf, num_bytes_read));
 }
 
 Exception InputFile::Close() {