[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

test/multi_node_test.py

@@ -24,7 +24,8 @@ def run_string_as_driver(driver_script):
     with tempfile.NamedTemporaryFile() as f:
         f.write(driver_script.encode("ascii"))
         f.flush()
-        out = subprocess.check_output([sys.executable, f.name]).decode("ascii")
+        out = ray.utils.decode(
+            subprocess.check_output([sys.executable, f.name]))
     return out