Convert actor dummy objects to task execution edges. (#1281)

* Define execution dependencies flatbuffer and add to Redis commands

* Convert TaskSpec to TaskExecutionSpec

* Add execution dependencies to Python bindings

* Submitting actor tasks uses execution dependency API instead of dummy argument

* Fix dependency getters and some cleanup for fetching missing dependencies

* C++ convention

* Make TaskExecutionSpec a C++ class

* Convert local scheduler to use TaskExecutionSpec class

* Convert some pointers to references

* Finish conversion to TaskExecutionSpec class

* fix

* Fix

* Fix memory errors?

* Cast flatbuffers GetSize to size_t

* Fixes

* add more retries in global scheduler unit test

* fix linting and cast fbb.GetSize to size_t

* Style and doc

* Fix linting and simplify from_flatbuf.

src/common/common_protocol.cc

@@ -13,6 +13,16 @@ ObjectID from_flatbuf(const flatbuffers::String &string) {
   return object_id;
 }
 
+const std::vector<ObjectID> from_flatbuf(
+    const flatbuffers::Vector<flatbuffers::Offset<flatbuffers::String>>
+        &vector) {
+  std::vector<ObjectID> object_ids;
+  for (int64_t i = 0; i < vector.Length(); i++) {
+    object_ids.push_back(from_flatbuf(*vector.Get(i)));
+  }
+  return object_ids;
+}
+
 flatbuffers::Offset<
     flatbuffers::Vector<flatbuffers::Offset<flatbuffers::String>>>
 to_flatbuf(flatbuffers::FlatBufferBuilder &fbb,
@@ -25,6 +35,17 @@ to_flatbuf(flatbuffers::FlatBufferBuilder &fbb,
   return fbb.CreateVector(results);
 }
 
+flatbuffers::Offset<
+    flatbuffers::Vector<flatbuffers::Offset<flatbuffers::String>>>
+to_flatbuf(flatbuffers::FlatBufferBuilder &fbb,
+           const std::vector<ObjectID> &object_ids) {
+  std::vector<flatbuffers::Offset<flatbuffers::String>> results;
+  for (auto object_id : object_ids) {
+    results.push_back(to_flatbuf(fbb, object_id));
+  }
+  return fbb.CreateVector(results);
+}
+
 std::string string_from_flatbuf(const flatbuffers::String &string) {
   return std::string(string.data(), string.size());
 }