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..c36e969118613a208ccf8605fe5cea9e4ff7cf77 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 +118,15 @@ void ImageWriterHandler::Cancel() {
   client_.reset();
 }
 
+bool ImageWriterHandler::ShouldResetImageWriter(const base::FilePath& image,
+                                                const base::FilePath& device) {
+  if (!image_writer_)

[dcheng, 2017/03/06 21:47:46]

Please link to the original bug and also comment here why it's important not to
reset if we're writing to the same image:

When writing and verifying the same image, it's important not to
close the file handles in between. Otherwise (insert reason from
original commit description)

[Noel Gordon, 2017/03/17 02:51:29]

Done.

+    return true;
+  if (image != image_writer_->GetImagePath())
+    return true;
+  if (device != image_writer_->GetDevicePath())
+    return true;
+  return false;
+}
+
 }  // namespace image_writer