IndexedDB: Remove IDBDatabaseBackendInterface/Proxy

Continued Source/web/*IDB* purging. This lets Source/modules
directly use the blink::WebIDBDatabase provided by the embedder.

The one subtle bit is a contract between Chromium and Blink
passing the WebIDBDatabase instance. In an upgrade scenario, 
onUpgradeNeeded(db) and onSuccess(db) are both called with
the same db object; obviously, the latter call is not an
ownership transfer. This was previously handled by re-using
the same refcounted proxy; now a flag is used and the pointer
is ignored. Once this lands we can update Chromium to pass null
in this case which will simplify both sides.

BUG=234277

Review URL: https://codereview.chromium.org/67503002

git-svn-id: svn://svn.chromium.org/blink/trunk@162569 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: refactor outline dialogs to run callback on item selection

This patch refactors outline dialogs to run specified callback on
item selection. This is a prework for the "jump to previous editing
location" feature.

BUG=281507

Review URL: https://codereview.chromium.org/77283005

git-svn-id: svn://svn.chromium.org/blink/trunk@162570 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Check the result of DocumentThreadableLoader::create in WorkerThreadableLoader::MainThreadBridge::mainThreadCreateLoader.

DocumentThreadableLoader::create may return 0 when the document loader has been already changed.
In the original code memory leak may happen when FileReader is runing in the worker thread and the user clicks the reload button because unsetPendingActivity will not be called.

BUG=none

Review URL: https://codereview.chromium.org/78393002

git-svn-id: svn://svn.chromium.org/blink/trunk@162571 bbb929c8-8fbe-4397-9dbb-9b2b20218538