Add debug methods to get the state of OlmSessions

I've been trying to track down issues with the OlmSessions getting out of sync
between two devices. To help with this, add a method which can be used from the
JS console to inspect the state of OlmSessions.

lib/OlmDevice.js

@@ -315,6 +315,38 @@ OlmDevice.prototype.getSessionIdForDevice = function(theirDeviceIdentityKey) {
     return sessionIds[0];
 };
 
+/**
+ * Get information on the active Olm sessions for a device.
+ * <p>
+ * Returns an array, with an entry for each active session. The first entry in
+ * the result will be the one used for outgoing messages. Each entry contains
+ * the keys 'hasReceivedMessage' (true if the session has received an incoming
+ * message and is therefore past the pre-key stage), and 'sessionId'.
+ *
+ * @param {string} deviceIdentityKey Curve25519 identity key for the device
+ * @return {Array.<{sessionId: string, hasReceivedMessage: Boolean}>}
+ */
+OlmDevice.prototype.getSessionInfoForDevice = function(deviceIdentityKey) {
+    var sessionIds = this.getSessionIdsForDevice(deviceIdentityKey);
+    sessionIds.sort();
+
+    var info = [];
+
+    function getSessionInfo(session) {
+        return {
+            hasReceivedMessage: session.has_received_message()
+        };
+    }
+
+    for (var i = 0; i < sessionIds.length; i++) {
+        var sessionId = sessionIds[i];
+        var res = this._getSession(deviceIdentityKey, sessionId, getSessionInfo);
+        res.sessionId = sessionId;
+        info.push(res);
+    }
+    return info;
+};
+
 /**
  * Encrypt an outgoing message using an existing session
  *

lib/crypto.js

@@ -488,6 +488,36 @@ Crypto.prototype.setDeviceVerification = function(userId, deviceId, verified, bl
 };
 
 
+/**
+ * Get information on the active olm sessions with a user
+ * <p>
+ * Returns a map from device id to an object with keys 'deviceIdKey' (the
+ * device's curve25519 identity key) and 'sessions' (an array of objects in the
+ * same format as that returned by {@link module:OlmDevice#getSessionInfoForDevice}).
+ * <p>
+ * This method is provided for debugging purposes.
+ *
+ * @param {string} userId id of user to inspect
+ *
+ * @return {Object.<string, {deviceIdKey: string, sessions: object[]}>}
+ */
+Crypto.prototype.getOlmSessionsForUser = function(userId) {
+    var devices = this.getStoredDevicesForUser(userId);
+    var result = {};
+    for (var j = 0; j < devices.length; ++j) {
+        var device = devices[j];
+        var deviceKey = device.getIdentityKey();
+        var sessions = this._olmDevice.getSessionInfoForDevice(deviceKey);
+
+        result[device.deviceId] = {
+            deviceIdKey: deviceKey,
+            sessions: sessions,
+        };
+    }
+    return result;
+};
+
+
 /**
  * Identify a device by curve25519 identity key and determine its verification state
  *