[fsp] Introduce BufferingFileStreamReader to read files in bigger chunks.

chrome/test/data/extensions/api_test/file_system_provider/big_file/test.js

Index: chrome/test/data/extensions/api_test/file_system_provider/big_file/test.js
diff --git a/chrome/test/data/extensions/api_test/file_system_provider/big_file/test.js b/chrome/test/data/extensions/api_test/file_system_provider/big_file/test.js
index 4ad2a36f0077cd19fd4919e19f3f88d2d4356d7e..2b3c758406de065fc72082c953b37e9c0d47b645 100644
--- a/chrome/test/data/extensions/api_test/file_system_provider/big_file/test.js
+++ b/chrome/test/data/extensions/api_test/file_system_provider/big_file/test.js
@@ -182,9 +182,9 @@ function onReadFileRequested(
 
   if (filePath == '/' + TESTING_6GB_FILE.name) {
     if (offset < TESTING_TEXT_OFFSET ||
-        offset + length > TESTING_TEXT_OFFSET + TESTING_TEXT.length) {
+        offset >= TESTING_TEXT_OFFSET + TESTING_TEXT.length) {
       console.error('Reading from a wrong location in the file!');
-      onError('INVALID_FAILED');  // enum ProviderError.
+      onError('FAILED');  // enum ProviderError.
       return;
     }