predictors: Don't initialize database after shutdown

PredictorDatabaseInternal::Initialize() can be called after the shutdown of
PredictorDatabase. In testing scenario it could lead to accessing a database
file in a directory that doesn't exist, because profile directories are deleted
after test.

This CL checks a cancellation flag that is set on PredictorDatabase shutdown
before opening a database file.

This CL also enables the predictor by default on ChromeOS since the disk I/O
issue should be resolved.

Bug: 839886
Change-Id: I27fbdda2cac282a44bd1bac962b27bf11de8520b
Reviewed-on: https://chromium-review.googlesource.com/1092851Reviewed-by: Egor Pasko <pasko@chromium.org>
Commit-Queue: Alexandr Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565983}

chrome/browser/predictors/loading_predictor_config.cc

@@ -39,15 +39,7 @@ const char kPreconnectMode[] = "preconnect";
 const char kNoPreconnectMode[] = "no-preconnect";
 
 const base::Feature kSpeculativePreconnectFeature{
-  kSpeculativePreconnectFeatureName,
-// TODO(https://crbug.com/839886): Enable the feature on ChromeOS after disk I/O
-// flakes are fixed.
-#if defined(OS_CHROMEOS)
-      base::FEATURE_DISABLED_BY_DEFAULT
-#else
-      base::FEATURE_ENABLED_BY_DEFAULT
-#endif
-};
+    kSpeculativePreconnectFeatureName, base::FEATURE_ENABLED_BY_DEFAULT};
 
 bool MaybeEnableSpeculativePreconnect(LoadingPredictorConfig* config) {
   if (!base::FeatureList::IsEnabled(kSpeculativePreconnectFeature))

chrome/browser/predictors/predictor_database.cc

@@ -97,6 +97,11 @@ void PredictorDatabaseInternal::Initialize() {
   DCHECK(db_task_runner_->RunsTasksInCurrentSequence());
   // TODO(tburkard): figure out if we need this.
   //  db_->set_exclusive_locking();
+  if (autocomplete_table_->IsCancelled() ||
+      resource_prefetch_tables_->IsCancelled()) {
+    return;
+  }
+
   bool success = db_->Open(db_path_);
 
   if (!success)

chrome/browser/predictors/predictor_table_base.cc

@@ -36,6 +36,10 @@ void PredictorTableBase::SetCancelled() {
   cancelled_.Set();
 }
 
+bool PredictorTableBase::IsCancelled() {
+  return cancelled_.IsSet();
+}
+
 sql::Connection* PredictorTableBase::DB() {
   DCHECK(db_task_runner_->RunsTasksInCurrentSequence());
   return db_;

chrome/browser/predictors/predictor_table_base.h

@@ -40,6 +40,7 @@ class PredictorTableBase
   virtual void LogDatabaseStats() = 0;
   void Initialize(sql::Connection* db);
   void SetCancelled();
+  bool IsCancelled();
   sql::Connection* DB();
   void ResetDB();