Closes #6724 (Allows object evaluation in devtools)

The purpose of this is to fix how objects were previously evaluated in
the developer tools.

- Before this, evaluating an object such as the `window` would `panic!`
- After this, evaluating an object such as the `window` outputs `[object
  Window]`

A few things to note:

- This commit contains `unsafe` code.
- This does not contain a test because the developer tools cannot be properly tested until #5971 lands.

components/devtools/actors/console.rs

@@ -8,6 +8,7 @@
 //! inspection, JS evaluation, autocompletion) in Servo.
 
 use actor::{Actor, ActorRegistry};
+use actors::object::ObjectActor;
 use protocol::JsonPacketStream;
 
 use devtools_traits::EvaluateJSReply::{NullValue, VoidValue, NumberValue};
@@ -92,7 +93,7 @@ impl Actor for ConsoleActor {
     }
 
     fn handle_message(&self,
-                      _registry: &ActorRegistry,
+                      registry: &ActorRegistry,
                       msg_type: &str,
                       msg: &json::Object,
                       stream: &mut TcpStream) -> Result<bool, ()> {
@@ -210,12 +211,14 @@ impl Actor for ConsoleActor {
                         }
                     }
                     StringValue(s) => s.to_json(),
-                    ActorValue(s) => {
-                        //TODO: make initial ActorValue message include these properties.
+                    ActorValue { class, uuid } => {
+                        //TODO: make initial ActorValue message include these properties?
                         let mut m = BTreeMap::new();
+                        let actor = ObjectActor::new(registry, uuid);
+
                         m.insert("type".to_string(), "object".to_string().to_json());
-                        m.insert("class".to_string(), "???".to_string().to_json());
-                        m.insert("actor".to_string(), s.to_json());
+                        m.insert("class".to_string(), class.to_json());
+                        m.insert("actor".to_string(), actor.to_json());
                         m.insert("extensible".to_string(), true.to_json());
                         m.insert("frozen".to_string(), false.to_json());
                         m.insert("sealed".to_string(), false.to_json());

components/devtools/actors/object.rs

@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use actor::{Actor, ActorRegistry};
+use rustc_serialize::json;
+use std::net::TcpStream;
+
+pub struct ObjectActor {
+    pub name: String,
+    pub uuid: String,
+}
+
+impl Actor for ObjectActor {
+    fn name(&self) -> String {
+        self.name.clone()
+    }
+    fn handle_message(&self,
+                      _: &ActorRegistry,
+                      _: &str,
+                      _: &json::Object,
+                      _: &mut TcpStream) -> Result<bool, ()> {
+        Ok(false)
+    }
+}
+
+impl ObjectActor {
+    pub fn new(registry: &ActorRegistry, uuid: String) -> String {
+        if !registry.script_actor_registered(uuid.clone()) {
+            let name = registry.new_name("object");
+            let actor = ObjectActor {
+                name: name.clone(),
+                uuid: uuid.clone(),
+            };
+
+            registry.register_script_actor(uuid, name.clone());
+            registry.register_later(box actor);
+
+            name
+        } else {
+            registry.script_to_actor(uuid)
+        }
+    }
+}

components/devtools/lib.rs

@@ -40,6 +40,7 @@ use actors::console::ConsoleActor;
 use actors::network_event::{NetworkEventActor, EventActor, ResponseStartMsg};
 use actors::framerate::FramerateActor;
 use actors::inspector::InspectorActor;
+use actors::object::ObjectActor;
 use actors::root::RootActor;
 use actors::tab::TabActor;
 use actors::timeline::TimelineActor;
@@ -68,13 +69,14 @@ mod actor;
 mod actors {
     pub mod console;
     pub mod framerate;
-    pub mod memory;
     pub mod inspector;
+    pub mod memory;
+    pub mod network_event;
+    pub mod object;
     pub mod root;
     pub mod tab;
     pub mod timeline;
     pub mod worker;
-    pub mod network_event;
 }
 mod protocol;