[fsp] Improve performance for reading small chunks of data.

webkit/browser/blob/blob_url_request_job.cc

Index: webkit/browser/blob/blob_url_request_job.cc
diff --git a/webkit/browser/blob/blob_url_request_job.cc b/webkit/browser/blob/blob_url_request_job.cc
index f1040f5dc651486ccae0428bbe8a9cc4d536fc1f..ba78a6fb18b0ed1324446de56692a6ec006c13f9 100644
--- a/webkit/browser/blob/blob_url_request_job.cc
+++ b/webkit/browser/blob/blob_url_request_job.cc
@@ -573,10 +573,13 @@ void BlobURLRequestJob::CreateFileStreamReader(size_t index,
       break;
     case BlobData::Item::TYPE_FILE_FILESYSTEM:
       reader = file_system_context_->CreateFileStreamReader(
-          fileapi::FileSystemURL(
-              file_system_context_->CrackURL(item.filesystem_url())),
-          item.offset() + additional_offset,
-          item.expected_modification_time()).release();
+                                         fileapi::FileSystemURL(
+                                             file_system_context_->CrackURL(
+                                                 item.filesystem_url())),
+                                         item.offset() + additional_offset,
+                                         item.length() - additional_offset,

[hashimoto, 2014/08/22 06:53:42]

BlobData::Item is typedef-ed to DataElement and DataElement is using uint64 to
store offset and length.
https://code.google.com/p/chromium/codesearch#chromium/src/webkit/common/data...

DataElement sets kuint64max to length if no value is provided when the data is
set.
I think you should replace int64 in FileStreamReader with uint64, or replace
uint64 in DataElement with int64 to make it work correctly.

The same goes for other parts.

[mtomasz, 2014/08/25 03:32:31]

This is a good point. However, int64 are used all over fileapi code, so I think
this should be fixed separately. Filed crbug.com/406967.

[hashimoto, 2014/09/01 11:01:01]

Then could you fix crbug.com/406967 first, or implement some check to places
where uint64->int64 conversion happens?

+                                         item.expected_modification_time())
+                   .release();
       break;
     default:
       NOTREACHED();