expose some meta data on a log export to show before submitting

src/logging/IDBLogger.js

@@ -163,6 +163,24 @@ class IDBLogExport {
         this._platform = platform;
     }
 
+    get minTimestamp() {
+        if (!this._items.length) {
+            return 0;
+        }
+        return this._items[0].start;
+    }
+
+    get maxTimestamp() {
+        if (!this._items.length) {
+            return 0;
+        }
+        return this._items[this._items.length - 1].end;
+    }
+
+    get count() {
+        return this._items.length;
+    }
+
     /**
      * @return {Promise}
      */