serial: Expose connection state for Bluetooth serial ports

Relevant spec change: WICG/serial#197

This CL adds a connected attribute to the SerialPort interface
that exposes the logical connection state of the serial port.
The behavior for Bluetooth serial ports is changed so that the
connect and disconnect events are dispatched when the connection
state of the Bluetooth device changes. The behavior is unchanged
for wired serial ports.

Intent to Prototype:
https://groups.google.com/a/chromium.org/g/blink-dev/c/dkz0IdP7kao

Bug: 1488031
Change-Id: I34b88246e62202c24eee08ad4a997aff7eadeebb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5039155
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1268876}

resources/chromium/fake-serial.js

@@ -356,6 +356,10 @@ class FakeSerialService {
       portInfo.hasUsbProductId = true;
       portInfo.usbProductId = info.usbProductId;
     }
+    portInfo.connected = true;
+    if (info?.connected !== undefined) {
+      portInfo.connected = info.connected;
+    }
 
     let token = ++this.nextToken_;
     portInfo.token = {high: 0n, low: BigInt(token)};
@@ -366,8 +370,10 @@ class FakeSerialService {
     };
     this.ports_.set(token, record);
 
-    for (let client of this.clients_) {
-      client.onPortAdded(portInfo);
+    if (portInfo.connected) {
+      for (let client of this.clients_) {
+        client.onPortConnectedStateChanged(portInfo);
+      }
     }
 
     return token;
@@ -381,8 +387,26 @@ class FakeSerialService {
 
     this.ports_.delete(token);
 
+    record.portInfo.connected = false;
+    for (let client of this.clients_) {
+      client.onPortConnectedStateChanged(record.portInfo);
+    }
+  }
+
+  setPortConnectedState(token, connected) {
+    let record = this.ports_.get(token);
+    if (record === undefined) {
+      return;
+    }
+
+    let was_connected = record.portInfo.connected;
+    if (was_connected === connected) {
+      return;
+    }
+
+    record.portInfo.connected = connected;
     for (let client of this.clients_) {
-      client.onPortRemoved(record.portInfo);
+      client.onPortConnectedStateChanged(record.portInfo);
     }
   }