Remove an unnecessary empty line misadded in r170022

TBR=ager

Review URL: https://codereview.chromium.org/212243002

git-svn-id: svn://svn.chromium.org/blink/trunk@170026 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove manual ref()-deref() in DatabaseContext.

DatabaseManager holds DatabaseContext references instead.

- We need to move DatabaseManager::registerDatabaseContext call from the
  constructor to the factory because registerDatabaseContext now increments the
  reference counter of a DatabaseContext and we can't update the reference
  counter in the constructor.

- We move DatabaseManager::unregisterDatabaseContext call from stopDatabases to
  contextDestroyed in order to match to deref() in the old code.

- We don't need m_isRegistered any longer because contextDestroyed is called
  just once. stopDatabases can be called twice.

- We need to move ~DatabaseManager implementation to DatabaseManager.cpp because
  we add RefPtr<DatabaseContext> in a member of DatabaseManager and
  ~DatabaseManager needs a complete definition of DatabaseContext.

BUG=347902

Review URL: https://codereview.chromium.org/212133002

git-svn-id: svn://svn.chromium.org/blink/trunk@170027 bbb929c8-8fbe-4397-9dbb-9b2b20218538