Start adding tests for LevelDBWrapper, and fix a bunch of bugs.

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index c46efd4abc24f44462bfc70947ed3ff8bd0f087e..d494cd5977f897448249c47eb4c287156a12ba85 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -1095,6 +1095,7 @@ test("content_unittests") {
     "../browser/indexed_db/mock_indexed_db_database_callbacks.h",
     "../browser/indexed_db/mock_indexed_db_factory.cc",
     "../browser/indexed_db/mock_indexed_db_factory.h",
+    "../browser/leveldb_wrapper_impl_unittest.cc",
     "../browser/loader/async_resource_handler_unittest.cc",
     "../browser/loader/async_revalidation_driver_unittest.cc",
     "../browser/loader/async_revalidation_manager_unittest.cc",
@@ -1384,6 +1385,8 @@ test("content_unittests") {
     "//cc/ipc",
     "//cc/surfaces",
     "//components/display_compositor",
+    "//components/leveldb/public/cpp",
+    "//components/leveldb/public/interfaces",
     "//components/payments:payment_app",
     "//components/rappor:test_support",
     "//content:resources",