Tweak leveldb options to reduce memory use

See https://groups.google.com/a/chromium.org/d/msg/storage-dev/7LPVIl2dx_M/-rQaqjCTDAAJ
for some data and discussion.

Bug: 793109
Change-Id: I342af261c094fbf26a934737b56960fb2c244011
Reviewed-on: https://chromium-review.googlesource.com/1026164Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Dan H <harringtond@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553741}

components/download/internal/background_service/download_store.cc

@@ -40,8 +40,11 @@ bool DownloadStore::IsInitialized() {
 
 void DownloadStore::Initialize(InitCallback callback) {
   DCHECK(!IsInitialized());
-  db_->Init(kDatabaseClientName, database_dir_,
-            leveldb_proto::CreateSimpleOptions(),
+  // These options reduce memory consumption.
+  leveldb_env::Options options = leveldb_proto::CreateSimpleOptions();
+  options.reuse_logs = false;
+  options.write_buffer_size = 64 << 10;  // 64 KiB
+  db_->Init(kDatabaseClientName, database_dir_, options,
             base::BindOnce(&DownloadStore::OnDatabaseInited,
                            weak_factory_.GetWeakPtr(), std::move(callback)));
 }

components/ntp_snippets/remote/remote_suggestions_database.cc

@@ -26,8 +26,7 @@ const char kImageDatabaseUMAClientName[] = "NTPSnippetImages";
 const char kSnippetDatabaseFolder[] = "snippets";
 const char kImageDatabaseFolder[] = "images";
 
-const size_t kDatabaseWriteBufferSizeBytes = 512 << 10;
-const size_t kDatabaseWriteBufferSizeBytesForLowEndDevice = 128 << 10;
+const size_t kDatabaseWriteBufferSizeBytes = 128 << 10;
 }  // namespace
 
 namespace ntp_snippets {
@@ -59,11 +58,9 @@ RemoteSuggestionsDatabase::RemoteSuggestionsDatabase(
       weak_ptr_factory_(this) {
   base::FilePath snippet_dir = database_dir.AppendASCII(kSnippetDatabaseFolder);
   leveldb_env::Options options = leveldb_proto::CreateSimpleOptions();
-  if (base::SysInfo::IsLowEndDevice()) {
-    options.write_buffer_size = kDatabaseWriteBufferSizeBytesForLowEndDevice;
-  } else {
-    options.write_buffer_size = kDatabaseWriteBufferSizeBytes;
-  }
+  options.reuse_logs = false;  // Consumes less RAM over time.
+  options.write_buffer_size = kDatabaseWriteBufferSizeBytes;
+
   database_->Init(kDatabaseUMAClientName, snippet_dir, options,
                   base::Bind(&RemoteSuggestionsDatabase::OnDatabaseInited,
                              weak_ptr_factory_.GetWeakPtr()));