[xray] Implement timeline and profiling API. (#2306)

* Add profile table and store profiling information there.

* Code for dumping timeline.

* Improve color scheme.

* Push timeline events on driver only for raylet.

* Improvements to profiling and timeline visualization

* Some linting

* Small fix.

* Linting

* Propagate node IP address through profiling events.

* Fix test.

* object_id.hex() should return byte string in python 2.

* Include gcs.fbs in node_manager.fbs.

* Remove flatbuffer definition duplication.

* Decode to unicode in Python 3 and bytes in Python 2.

* Minor

* Submit profile events in a batch. Revert some CMake changes.

* Fix

* Workaround test failure.

* Fix linting

* Linting

* Don't return anything from chrome_tracing_dump when filename is provided.

* Remove some redundancy from profile table.

* Linting

* Move TODOs out of docstring.

* Minor

python/ray/__init__.py

@@ -48,7 +48,7 @@ except ImportError as e:
 
 from ray.local_scheduler import ObjectID, _config  # noqa: E402
 from ray.worker import (error_info, init, connect, disconnect, get, put, wait,
-                        remote, log_event, log_span, flush_log, get_gpu_ids,
+                        remote, profile, flush_profile_data, get_gpu_ids,
                         get_resource_ids, get_webui_url,
                         register_custom_serializer)  # noqa: E402
 from ray.worker import (SCRIPT_MODE, WORKER_MODE, PYTHON_MODE,
@@ -65,7 +65,7 @@ __version__ = "0.4.0"
 
 __all__ = [
     "error_info", "init", "connect", "disconnect", "get", "put", "wait",
-    "remote", "log_event", "log_span", "flush_log", "actor", "method",
+    "remote", "profile", "flush_profile_data", "actor", "method",
     "get_gpu_ids", "get_resource_ids", "get_webui_url",
     "register_custom_serializer", "SCRIPT_MODE", "WORKER_MODE", "PYTHON_MODE",
     "SILENT_MODE", "global_state", "ObjectID", "_config", "__version__"