Delete unused BaseMultiplexedRequestHandler
Fix GlobalView class inheritance
Fix clone method in EmptyEntity; also make it a const singleton
Add missing members to _ErrorEntity
Fix typo in tracing.dart
Cleanup transforms.dart
Move _runZonedWithOnDone to the new zone API
Fix types in IndexedDbCache
Fix types in tests
Type check test fixes
Set content-type iff request has payload
Merge pull request #117 from yjbanov/code-cleanup

Another round of code clean-up; see individual commits for details