Add support for launching devtools server on random port

Assign random port to devtools server in case user does not specify a
port explicitly and report it to the embedding layer for display to user.

ports/glutin/browser.rs

@@ -515,6 +515,12 @@ where
                     debug!("MediaSessionEvent received");
                     // TODO(ferjm): MediaSession support for Glutin based browsers.
                 },
+                EmbedderMsg::OnDevtoolsStarted(port) => {
+                    match port {
+                        Ok(p) => info!("Devtools Server running on port {}", p),
+                        Err(()) => error!("Error running devtools server"),
+                    }
+                },
             }
         }
     }

ports/libmlservo/src/lib.rs

@@ -423,6 +423,13 @@ impl HostTrait for HostCallbacks {
     }
 
     fn set_clipboard_contents(&self, _contents: String) {}
+
+    fn on_devtools_started(&self, port: Result<u16, ()>) {
+        match port {
+            Ok(p) => info!("Devtools Server running on port {}", p),
+            Err(()) => error!("Error running Devtools server"),
+        }
+    }
 }
 
 pub struct ServoInstance {

ports/libsimpleservo/api/src/lib.rs

@@ -146,6 +146,8 @@ pub trait HostTrait {
     fn on_media_session_playback_state_change(&self, state: MediaSessionPlaybackState);
     /// Called when the media session position state is set.
     fn on_media_session_set_position_state(&self, duration: f64, position: f64, playback_rate: f64);
+    /// Called when devtools server is started
+    fn on_devtools_started(&self, port: Result<u16, ()>);
 }
 
 pub struct ServoGlue {
@@ -670,6 +672,9 @@ impl ServoGlue {
                             ),
                     };
                 },
+                EmbedderMsg::OnDevtoolsStarted(port) => {
+                    self.callbacks.host_callbacks.on_devtools_started(port);
+                },
                 EmbedderMsg::Status(..) |
                 EmbedderMsg::SelectFiles(..) |
                 EmbedderMsg::MoveTo(..) |

ports/libsimpleservo/capi/src/lib.rs

@@ -23,7 +23,7 @@ use simpleservo::{
 use std::ffi::{CStr, CString};
 #[cfg(target_os = "windows")]
 use std::mem;
-use std::os::raw::{c_char, c_void};
+use std::os::raw::{c_char, c_uint, c_void};
 use std::panic::{self, UnwindSafe};
 use std::slice;
 use std::str::FromStr;
@@ -229,6 +229,7 @@ pub struct CHostCallbacks {
         default: *const c_char,
         trusted: bool,
     ) -> *const c_char,
+    pub on_devtools_started: extern "C" fn(result: CDevtoolsServerState, port: c_uint),
 }
 
 /// Servo options
@@ -286,6 +287,12 @@ pub enum CMediaSessionPlaybackState {
     Paused,
 }
 
+#[repr(C)]
+pub enum CDevtoolsServerState {
+    Started,
+    Error,
+}
+
 impl From<MediaSessionPlaybackState> for CMediaSessionPlaybackState {
     fn from(state: MediaSessionPlaybackState) -> Self {
         match state {
@@ -854,4 +861,17 @@ impl HostTrait for HostCallbacks {
         let contents_str = c_str.to_str().expect("Can't create str");
         Some(contents_str.to_owned())
     }
+
+    fn on_devtools_started(&self, port: Result<u16, ()>) {
+        match port {
+            Ok(p) => {
+                info!("Devtools Server running on port {}", p);
+                (self.0.on_devtools_started)(CDevtoolsServerState::Started, p.into());
+            },
+            Err(()) => {
+                error!("Error running devtools server");
+                (self.0.on_devtools_started)(CDevtoolsServerState::Error, 0);
+            },
+        }
+    }
 }

ports/libsimpleservo/jniapi/src/lib.rs

@@ -603,6 +603,13 @@ impl HostTrait for HostCallbacks {
         )
         .unwrap();
     }
+
+    fn on_devtools_started(&self, port: Result<u16, ()>) {
+        match port {
+            Ok(p) => info!("Devtools Server running on port {}", p),
+            Err(()) => error!("Error running devtools server"),
+        }
+    }
 }
 
 fn initialize_android_glue(env: &JNIEnv, activity: JObject) {