Generate OnPipelineSeeked event for seek to currenttime in pause state

Pipeline generates OnPipelineSeeked and OnPipelineBufferingStateChanged
events in response to seek operations. There is an event generated already
for OnPipelineBufferingStateChanged but missing one for OnPipelineSeeked.

Follow up fix for https://codereview.chromium.org/740663002/
Required for landing https://codereview.chromium.org/456343002/

Review URL: https://codereview.chromium.org/791233003

Cr-Commit-Position: refs/heads/master@{#308263}

media/blink/webmediaplayer_impl.cc

@@ -327,16 +327,19 @@ void WebMediaPlayerImpl::seek(double seconds) {
 
   // Update our paused time.
   // In paused state ignore the seek operations to current time and generate
-  // buffer state change event to eventually fire seeking and seeked events
+  // OnPipelineSeeked and OnPipelineBufferingStateChanged events
+  // to eventually fire seeking and seeked events
   if (paused_) {
     if (paused_time_ != seek_time) {
       paused_time_ = seek_time;
     } else {
+      main_task_runner_->PostTask(
+          FROM_HERE, base::Bind(&WebMediaPlayerImpl::OnPipelineSeeked,
+                                AsWeakPtr(), false, PIPELINE_OK));
       main_task_runner_->PostTask(
           FROM_HERE,
           base::Bind(&WebMediaPlayerImpl::OnPipelineBufferingStateChanged,
-                     AsWeakPtr(),
-                     BUFFERING_HAVE_ENOUGH));
+                     AsWeakPtr(), BUFFERING_HAVE_ENOUGH));
       return;
     }
   }