fix: -Wunsafe-buffer-usage warnings in Clipboard::WriteBuffer() (#43795)

* fix: -Wunsafe-buffer-usage warnings in Clipboard::WriteBuffer()

* chore: add a DCHECK to confirm the BigBuffer is full

shell/common/api/electron_api_clipboard.cc

@@ -111,12 +111,16 @@ void Clipboard::WriteBuffer(const std::string& format,
     return;
   }
 
+  CHECK(buffer->IsArrayBufferView());
+  v8::Local<v8::ArrayBufferView> buffer_view = buffer.As<v8::ArrayBufferView>();
+  const size_t n_bytes = buffer_view->ByteLength();
+  mojo_base::BigBuffer big_buffer{n_bytes};
+  [[maybe_unused]] const size_t n_got =
+      buffer_view->CopyContents(big_buffer.data(), n_bytes);
+  DCHECK_EQ(n_got, n_bytes);
+
   ui::ScopedClipboardWriter writer(GetClipboardBuffer(args));
-  base::span<const uint8_t> payload_span(
-      reinterpret_cast<const uint8_t*>(node::Buffer::Data(buffer)),
-      node::Buffer::Length(buffer));
-  writer.WriteUnsafeRawData(base::UTF8ToUTF16(format),
-                            mojo_base::BigBuffer(payload_span));
+  writer.WriteUnsafeRawData(base::UTF8ToUTF16(format), std::move(big_buffer));
 }
 
 void Clipboard::Write(const gin_helper::Dictionary& data,