Added timer to explore v2 and share it with sqllab (#1802)

* Added timer to explore v2 and share it with sqllab

* Fixed js tests

* Add timer to initial load

* Make timer smaller

* nits

superset/assets/javascripts/components/Timer.jsx

@@ -0,0 +1,71 @@
+import React from 'react';
+import { now, fDuration } from '../modules/dates';
+
+class Timer extends React.PureComponent {
+  constructor(props) {
+    super(props);
+    this.state = {
+      clockStr: '',
+    };
+  }
+  componentWillMount() {
+    this.startTimer();
+  }
+  componentWillUnmount() {
+    this.stopTimer();
+  }
+  startTimer() {
+    if (!(this.timer)) {
+      this.timer = setInterval(this.stopwatch.bind(this), 30);
+    }
+  }
+  stopTimer() {
+    clearInterval(this.timer);
+    this.timer = null;
+  }
+  stopwatch() {
+    if (this.props && this.props.startTime) {
+      const endDttm = this.props.endTime || now();
+      if (this.props.startTime < endDttm) {
+        const clockStr = fDuration(this.props.startTime, endDttm);
+        this.setState({ clockStr });
+      }
+      if (!this.props.isRunning) {
+        this.stopTimer();
+      }
+    }
+  }
+  render() {
+    if (this.props && this.props.isRunning) {
+      this.startTimer();
+    }
+    let timerSpan = null;
+    if (this.props) {
+      timerSpan = (
+        <span
+          className={`inlineBlock m-r-5 label label-${this.props.status}`}
+          style={this.props.style}
+        >
+          {this.state.clockStr}
+        </span>
+      );
+    }
+    return timerSpan;
+  }
+}
+Timer.propTypes = {
+  startTime: React.PropTypes.number,
+  endTime: React.PropTypes.number,
+  isRunning: React.PropTypes.bool.isRequired,
+  status: React.PropTypes.string,
+  style: React.PropTypes.object,
+};
+
+Timer.defaultProps = {
+  startTime: null,
+  endTime: null,
+  status: 'success',
+  style: null,
+};
+
+export default Timer;