Support earliest seekable time in WMPI.

content/renderer/media/webmediaplayer_ms.cc

Index: content/renderer/media/webmediaplayer_ms.cc
diff --git a/content/renderer/media/webmediaplayer_ms.cc b/content/renderer/media/webmediaplayer_ms.cc
index 586f180129ec1f748ad9e741ecc1936dcd7fdc93..551dbeeb5a2e1a772af24f0f8d0c7cbfaddcd6f4 100644
--- a/content/renderer/media/webmediaplayer_ms.cc
+++ b/content/renderer/media/webmediaplayer_ms.cc
@@ -248,6 +248,10 @@ bool WebMediaPlayerMS::seeking() const {
   return false;
 }
 
+double WebMediaPlayerMS::earliestTime() const {
+  return 0;
+}
+
 double WebMediaPlayerMS::duration() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return std::numeric_limits<double>::infinity();