Tiny: Post PerformFullHashCheck on IO thread, instead of calling it synchronously.

components/safe_browsing_db/v4_local_database_manager_unittest.cc

Index: components/safe_browsing_db/v4_local_database_manager_unittest.cc
diff --git a/components/safe_browsing_db/v4_local_database_manager_unittest.cc b/components/safe_browsing_db/v4_local_database_manager_unittest.cc
index 4c572bc4f110a8ec8305b8d21d39694e639abf17..f51e5358ca3df2c8d60160596944321de8d4d886 100644
--- a/components/safe_browsing_db/v4_local_database_manager_unittest.cc
+++ b/components/safe_browsing_db/v4_local_database_manager_unittest.cc
@@ -205,6 +205,9 @@ TEST_F(V4LocalDatabaseManagerTest, TestCheckBrowseUrlWithFakeDbReturnsMatch) {
   // The fake database returns a matched hash prefix.
   EXPECT_FALSE(v4_local_database_manager_->CheckBrowseUrl(
       GURL("http://example.com/a/"), nullptr));
+
+  // Wait for PerformFullHashCheck to complete.
+  WaitForTasksOnTaskRunner();
 }
 
 TEST_F(V4LocalDatabaseManagerTest,