Update memory file stream reader to behave like local

As I'm adding a 4th file stream reader unittest, I thought I would
combine all of the similar-but-not-exactly-the-same sets of file stream
reader unittests.  This is one behavior difference between all of the
file stream readers, so I thought I would clean it up first.

This return value is how file system file stream reader and local file
stream reader behave when seeking past the end.

Change-Id: Ife39c7c82b8aee161dd26aa67e001c09e93d30ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2406703
Commit-Queue: enne <enne@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Auto-Submit: enne <enne@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806395}

storage/browser/file_system/memory_file_stream_reader_unittest.cc

@@ -235,7 +235,8 @@ TEST_F(MemoryFileStreamReaderTest, ReadWithNegativeOffset) {
   int result = 0;
   std::string data;
   ReadFromReader(reader.get(), &data, 1, &result);
-  ASSERT_EQ(net::ERR_REQUEST_RANGE_NOT_SATISFIABLE, result);
+  ASSERT_EQ(net::ERR_INVALID_ARGUMENT, result);
+  ASSERT_EQ(data.size(), 0u);
 }
 
 TEST_F(MemoryFileStreamReaderTest, ReadWithOffsetLargerThanFile) {
@@ -244,7 +245,8 @@ TEST_F(MemoryFileStreamReaderTest, ReadWithOffsetLargerThanFile) {
   int result = 0;
   std::string data;
   ReadFromReader(reader.get(), &data, 1, &result);
-  ASSERT_EQ(net::ERR_REQUEST_RANGE_NOT_SATISFIABLE, result);
+  ASSERT_EQ(net::OK, result);
+  ASSERT_EQ(data.size(), 0u);
 }
 
 }  // namespace storage

storage/browser/file_system/obfuscated_file_util_memory_delegate.cc

@@ -456,8 +456,13 @@ int ObfuscatedFileUtilMemoryDelegate::ReadFile(const base::FilePath& path,
     return net::ERR_FILE_NOT_FOUND;
 
   int64_t remaining = dp->entry->file_content.size() - offset;
-  if (offset < 0 || remaining < 0)
-    return net::ERR_REQUEST_RANGE_NOT_SATISFIABLE;
+  if (offset < 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)
+    return 0;
 
   if (buf_len > remaining)
     buf_len = static_cast<int>(remaining);