[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/utils.py

@@ -170,6 +170,8 @@ def random_string():
 
 def decode(byte_str):
     """Make this unicode in Python 3, otherwise leave it as bytes."""
+    if not isinstance(byte_str, bytes):
+        raise ValueError("The argument must be a bytes object.")
     if sys.version_info >= (3, 0):
         return byte_str.decode("ascii")
     else: