Reduce copy on QuotaFileIO::Write

webkit/plugins/ppapi/quota_file_io.cc

Index: webkit/plugins/ppapi/quota_file_io.cc
diff --git a/webkit/plugins/ppapi/quota_file_io.cc b/webkit/plugins/ppapi/quota_file_io.cc
index 84c44e3e833bdea0e8b55073ed7b1288e54d38ca..dc768fae25d217bcdfee22e6d364bfb222e9eee0 100644
--- a/webkit/plugins/ppapi/quota_file_io.cc
+++ b/webkit/plugins/ppapi/quota_file_io.cc
@@ -11,6 +11,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop_proxy.h"
 #include "base/stl_util.h"
+#include "base/task_runner_util.h"
 #include "webkit/plugins/ppapi/host_globals.h"
 #include "webkit/plugins/ppapi/ppapi_plugin_instance.h"
 #include "webkit/plugins/ppapi/resource_helper.h"
@@ -100,10 +101,13 @@ class QuotaFileIO::WriteOperation : public PendingOperationBase {
       return;
     }
 
-    if (!base::FileUtilProxy::Write(
-            plugin_delegate->GetFileThreadMessageLoopProxy(),
-            quota_io_->file_, offset_, buffer_.get(), bytes_to_write_,
-            base::Bind(&WriteOperation::DidFinish,
+    if (!base::PostTaskAndReplyWithResult(
+            plugin_delegate->GetFileThreadMessageLoopProxy(), FROM_HERE,
+            base::Bind(&base::WritePlatformFile,
+                       quota_io_->file_, offset_,
+                       base::Owned(buffer_.release()),
+                       bytes_to_write_),
+            base::Bind(&WriteOperation::DidWrite,
                        weak_factory_.GetWeakPtr()))) {
       DidFail(base::PLATFORM_FILE_ERROR_FAILED);
       return;
@@ -123,6 +127,12 @@ class QuotaFileIO::WriteOperation : public PendingOperationBase {
   }
 
  private:
+  void DidWrite(int bytes_written) {
+    base::PlatformFileError error = bytes_written >= 0 ?

[brettw, 2013/01/09 20:17:10]

What happens if you write 0 bytes? It looks like before this may have succeeded,
and now it will report failure.

[tzik, 2013/01/10 04:02:36]

Right, this changes its behavior for 0-byte write.
Fixed.

+        base::PLATFORM_FILE_OK : base::PLATFORM_FILE_ERROR_FAILED;
+    DidFinish(error, bytes_written);
+  }
+
   void DidFinish(PlatformFileError status, int bytes_written) {
     finished_ = true;
     status_ = status;