[Paint Preview] Allow a partial capture success to pass

Minor change. Allows partial success status to count as a success. This
means one or more subframes were unable to be captured. Usually this is
due to a subframe not being loaded (e.g. lazily loaded iframe). This
loss in fidelity is usually minor and acceptable.

Change-Id: I65a4ca2d0e366e4b93bfede7212b45ff2f6d7fd8
Bug: 1084657
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2211914Reviewed-by: Mehran Mahmoudi <mahmoudi@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771624}

components/paint_preview/browser/paint_preview_base_service.cc

@@ -148,7 +148,9 @@ void PaintPreviewBaseService::OnCaptured(
   if (web_contents)
     web_contents->DecrementCapturerCount(true);
 
-  if (status != mojom::PaintPreviewStatus::kOk || !proto) {
+  if (!(status == mojom::PaintPreviewStatus::kOk ||
+        status == mojom::PaintPreviewStatus::kPartialSuccess) ||
+      !proto) {
     DVLOG(1) << "ERROR: Paint Preview failed to capture for document "
              << guid.ToString() << " with error " << status;
     std::move(callback).Run(kCaptureFailed, nullptr);