[FileAPI] Fix CHECK failure if renderer sends zero-sized bytes element.

Bug: 1114898
Change-Id: I0b527a8fdc2dd4d5fcb5b9eb7140fa8ac4faa069
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2347921
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796935}

storage/browser/blob/blob_registry_impl.cc

@@ -372,8 +372,10 @@ void BlobRegistryImpl::BlobUnderConstruction::ResolvedAllBlobDependencies() {
   for (const auto& entry : elements_) {
     auto& element = entry.element;
     if (element->is_bytes()) {
+      if (element->get_bytes()->length > 0) {
         transport_strategy_->AddBytesElement(element->get_bytes().get(),
                                              entry.bytes_provider);
+      }
     } else if (element->is_file()) {
       const auto& f = element->get_file();
       builder_->AppendFile(

storage/browser/blob/blob_registry_impl_unittest.cc

@@ -294,6 +294,37 @@ TEST_F(BlobRegistryImplTest, Register_EmptyBlob) {
   EXPECT_EQ(0u, BlobsUnderConstruction());
 }
 
+TEST_F(BlobRegistryImplTest, Register_EmptyBytesBlob) {
+  const std::string kId = "id";
+  const std::string kContentType = "content/type";
+  const std::string kContentDisposition = "disposition";
+
+  std::vector<blink::mojom::DataElementPtr> elements;
+  elements.push_back(
+      blink::mojom::DataElement::NewBytes(blink::mojom::DataElementBytes::New(
+          0, base::nullopt, CreateBytesProvider(""))));
+
+  mojo::Remote<blink::mojom::Blob> blob;
+  EXPECT_TRUE(registry_->Register(blob.BindNewPipeAndPassReceiver(), kId,
+                                  kContentType, kContentDisposition,
+                                  std::move(elements)));
+
+  EXPECT_TRUE(bad_messages_.empty());
+
+  EXPECT_EQ(kId, UUIDFromBlob(blob.get()));
+  EXPECT_TRUE(context_->registry().HasEntry(kId));
+  std::unique_ptr<BlobDataHandle> handle = context_->GetBlobDataFromUUID(kId);
+  EXPECT_EQ(kContentType, handle->content_type());
+  EXPECT_EQ(kContentDisposition, handle->content_disposition());
+  EXPECT_EQ(0u, handle->size());
+
+  WaitForBlobCompletion(handle.get());
+
+  EXPECT_FALSE(handle->IsBroken());
+  EXPECT_EQ(BlobStatus::DONE, handle->GetBlobStatus());
+  EXPECT_EQ(0u, BlobsUnderConstruction());
+}
+
 TEST_F(BlobRegistryImplTest, Register_ReferencedBlobClosedPipe) {
   const std::string kId = "id";