[Offline Pages] Download UI: Remove all observers when clearing cache.

components/offline_pages/core/downloads/download_ui_adapter.cc

Index: components/offline_pages/core/downloads/download_ui_adapter.cc
diff --git a/components/offline_pages/core/downloads/download_ui_adapter.cc b/components/offline_pages/core/downloads/download_ui_adapter.cc
index 118efd999d448fbfa05af0708044a97edab37698..bfc4526f042d79150909c6d5a2646569eaa5a38b 100644
--- a/components/offline_pages/core/downloads/download_ui_adapter.cc
+++ b/components/offline_pages/core/downloads/download_ui_adapter.cc
@@ -203,8 +203,10 @@ void DownloadUIAdapter::LoadCache() {
 void DownloadUIAdapter::ClearCache() {
   // Once loaded, this class starts to observe the model. Only remove observer
   // if it was added.
-  if (state_ == State::LOADED)
+  if (state_ == State::LOADED) {
     model_->RemoveObserver(this);
+    request_coordinator_->RemoveObserver(this);
+  }
   items_.clear();
   state_ = State::NOT_LOADED;
 }