https://bugs.webkit.org/show_bug.cgi?id=125127

Reviewed by Darin Adler.

Add a non-main WorkQueue to the DatabaseProcess:
* DatabaseProcess/DatabaseProcess.cpp:
(WebKit::DatabaseProcess::DatabaseProcess):
(WebKit::DatabaseProcess::queue):
* DatabaseProcess/DatabaseProcess.h:

* DatabaseProcess/IndexedDB/UniqueIDBDatabase.cpp:
(WebKit::UniqueIDBDatabase::UniqueIDBDatabase):
(WebKit::UniqueIDBDatabase::enqueueDatabaseQueueRequest): Add an AsyncRequest to the deque then schedule performing
  the requests on the background WorkQueue.
(WebKit::UniqueIDBDatabase::processDatabaseRequestQueue): Processes all enqueued database requests.
(WebKit::UniqueIDBDatabase::getOrEstablishIDBDatabaseMetadata): Renamed from getIDBDatabaseMetadata().
(WebKit::UniqueIDBDatabase::getOrEstablishIDBDatabaseMetadataInternal): For doing i/o on a background queue/thread.
* DatabaseProcess/IndexedDB/UniqueIDBDatabase.h:

Add a creator that takes the abort handler as an argument, and rename requestedCompleted()
to completeRequest(). This makes more sense in more situations:
* Shared/AsyncRequest.cpp:
(WebKit::AsyncRequest::AsyncRequest):
(WebKit::AsyncRequest::setAbortHandler):
* Shared/AsyncRequest.h:
(WebKit::AsyncRequest::completeRequest):

Update for the AsyncRequest rename:
* WebProcess/Databases/IndexedDB/WebIDBServerConnection.cpp:
(WebKit::WebIDBServerConnection::didGetOrEstablishIDBDatabaseMetadata):

* DatabaseProcess/IndexedDB/DatabaseProcessIDBConnection.cpp:
(WebKit::DatabaseProcessIDBConnection::getOrEstablishIDBDatabaseMetadata):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160033 268f45cc-cd09-0410-ab3c-d52691b4dbfc