This changes is part of a large patch for easier review. Try the whole patch in one go by checking out https://github.com/chinmaygarde/flutter_engine/tree/shell directly. This patch contains the following changes:
* blink::DartVM (instead of the old dart_init.cc) manages all the VM instance.
* blink::DartIsolate is the C++ object references by the shell for interacting with Dart isolates. The only strong referneces to these objects are in the VM.
* blink::DartSnapshot objects can resolve the appropriate dart snapshot data from various sources and own referneces to these snapshots that can be collected when the isolate or VM goes away.
* blink::ServiceProtocol manages the service protocol endpoints that the engine cares about and provides endpoints for out of the box. Also provides hooks for custom endpoints used as necessary by different platforms.
* Unit tests for testing the VM and isolates in isolation.
* Asset font selecto peeks into the unified asset manager for font manifests instead of specific asset resolvers.