PDF Thumbnails: address comments from cl/2417790

Part 2 of 2:
Clean up mojo bound and call flow. reset() the pdf_thumbnailer_ when
the server replies with a Bitmap to make the code robust to server
errors (ignore disconnects) during post-processing of the Bitmap.

Bug: 1129607
No-try: true
Change-Id: I7dbbdecc667116c4d2a56e630b9f54162fb47279
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2426628
Commit-Queue: Bo Majewski <majewski@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810462}

chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc

@@ -1229,14 +1229,12 @@ void FileManagerPrivateInternalGetThumbnailFunction::FetchPdfThumbnail(
     return;
   }
   memcpy(pdf_region.mapping.memory(), content.data(), content.size());
-  if (!pdf_thumbnailer_.is_bound()) {
+  DCHECK(!pdf_thumbnailer_.is_bound());
   GetPrintingService()->BindPdfThumbnailer(
       pdf_thumbnailer_.BindNewPipeAndPassReceiver());
-    pdf_thumbnailer_.set_disconnect_handler(
-        base::BindOnce(&FileManagerPrivateInternalGetThumbnailFunction::
-                           PdfThumbnailDisconected,
+  pdf_thumbnailer_.set_disconnect_handler(base::BindOnce(
+      &FileManagerPrivateInternalGetThumbnailFunction::PdfThumbnailDisconected,
       base::Unretained(this)));
-  }
   gfx::Size thumb_size =
       crop_to_square
           ? gfx::Size(FileManagerPrivateInternalGetThumbnailFunction::kSize,
@@ -1263,6 +1261,7 @@ void FileManagerPrivateInternalGetThumbnailFunction::PdfThumbnailDisconected() {
 void FileManagerPrivateInternalGetThumbnailFunction::GotPdfThumbnail(
     const SkBitmap& bitmap) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  pdf_thumbnailer_.reset();
   base::ThreadPool::PostTaskAndReplyWithResult(
       FROM_HERE, base::BindOnce(&ConvertAndEncode, bitmap),
       base::BindOnce(