ImageWriter: Add ShouldResetImageWriter helper

chrome/utility/image_writer/image_writer_handler.cc

Index: chrome/utility/image_writer/image_writer_handler.cc
diff --git a/chrome/utility/image_writer/image_writer_handler.cc b/chrome/utility/image_writer/image_writer_handler.cc
index d63edb7705fc684abbba908d632d5d104be4ee4b..437f50c581f26aff37a05c586e31416dee2f2447 100644
--- a/chrome/utility/image_writer/image_writer_handler.cc
+++ b/chrome/utility/image_writer/image_writer_handler.cc
@@ -42,11 +42,8 @@ void ImageWriterHandler::Write(
   if (test_mode)
     target_device = MakeTestDevicePath(image);
 
-  // https://crbug.com/352442
-  if (!image_writer_.get() || image != image_writer_->GetImagePath() ||
-      target_device != image_writer_->GetDevicePath()) {
+  if (ShouldResetImageWriter(image, target_device))
     image_writer_.reset(new ImageWriter(this, image, target_device));
-  }
 
   if (image_writer_->IsRunning()) {
     SendFailed(error::kOperationAlreadyInProgress);
@@ -80,11 +77,8 @@ void ImageWriterHandler::Verify(
   if (test_mode)
     target_device = MakeTestDevicePath(image);
 
-  // https://crbug.com/352442
-  if (!image_writer_.get() || image != image_writer_->GetImagePath() ||
-      target_device != image_writer_->GetDevicePath()) {
+  if (ShouldResetImageWriter(image, target_device))
     image_writer_.reset(new ImageWriter(this, image, target_device));
-  }
 
   if (image_writer_->IsRunning()) {
     SendFailed(error::kOperationAlreadyInProgress);
@@ -124,4 +118,19 @@ void ImageWriterHandler::Cancel() {
   client_.reset();
 }
 
+bool ImageWriterHandler::ShouldResetImageWriter(const base::FilePath& image,
+                                                const base::FilePath& device) {
+  if (!image_writer_)
+    return true;
+  if (image != image_writer_->GetImagePath())
+    return true;
+  if (device != image_writer_->GetDevicePath())
+    return true;
+
+  // When writing and verifying the same file on the same device, keep
+  // the file handles open; do not reset them since that can cause the
+  // operation to fail in unexpected ways: crbug.com/352442#c7
+  return false;
+}
+
 }  // namespace image_writer