Implement throttling behavior for LocalStorage mojo messages.

content/renderer/dom_storage/local_storage_cached_area.cc

Index: content/renderer/dom_storage/local_storage_cached_area.cc
diff --git a/content/renderer/dom_storage/local_storage_cached_area.cc b/content/renderer/dom_storage/local_storage_cached_area.cc
index 379394c4f2a39dc079d7021717e26460668c4cba..662da6697247726fc4c210a2d4b776d3c55a46cf 100644
--- a/content/renderer/dom_storage/local_storage_cached_area.cc
+++ b/content/renderer/dom_storage/local_storage_cached_area.cc
@@ -83,6 +83,7 @@ LocalStorageCachedArea::LocalStorageCachedArea(
       cached_areas_(cached_areas), weak_factory_(this) {
   storage_partition_service->OpenLocalStorage(origin_,
                                               mojo::MakeRequest(&leveldb_));
+  leveldb_.set_process_async_during_sync(true);
   mojom::LevelDBObserverAssociatedPtrInfo ptr_info;
   binding_.Bind(&ptr_info, leveldb_.associated_group());
   leveldb_->AddObserver(std::move(ptr_info));
@@ -128,6 +129,8 @@ bool LocalStorageCachedArea::SetItem(const base::string16& key,
                 PackSource(page_url, storage_area_id),
                 base::Bind(&LocalStorageCachedArea::OnSetItemComplete,
                            weak_factory_.GetWeakPtr(), key));
+  FlushIfNeeded();
+
   return true;
 }
 
@@ -145,18 +148,19 @@ void LocalStorageCachedArea::RemoveItem(const base::string16& key,
                    PackSource(page_url, storage_area_id),
                    base::Bind(&LocalStorageCachedArea::OnRemoveItemComplete,
                               weak_factory_.GetWeakPtr(), key));
+  FlushIfNeeded();
 }
 
 void LocalStorageCachedArea::Clear(const GURL& page_url,
                                    const std::string& storage_area_id) {
   // No need to prime the cache in this case.
-
   Reset();
   map_ = new DOMStorageMap(kPerStorageAreaQuota);
   ignore_all_mutations_ = true;
   leveldb_->DeleteAll(PackSource(page_url, storage_area_id),
                       base::Bind(&LocalStorageCachedArea::OnClearComplete,
                                   weak_factory_.GetWeakPtr()));
+  FlushIfNeeded();
 }
 
 void LocalStorageCachedArea::AreaCreated(LocalStorageArea* area) {
@@ -323,6 +327,13 @@ void LocalStorageCachedArea::EnsureLoaded() {
   }
 }
 
+void LocalStorageCachedArea::FlushIfNeeded() {
+  if (leveldb_.pending_callback_count() > 1000) {
+    leveldb_->FlushPipe();
+    DCHECK_EQ(0u, leveldb_.pending_callback_count());
+  }
+}
+
 void LocalStorageCachedArea::OnSetItemComplete(const base::string16& key,
                                                bool success) {
   if (!success) {