Fix timeline segment position calculation

Bug: 812531
Change-Id: I0a9d54b28ef7e17d94358a692f7a2259130210a1
Reviewed-on: https://chromium-review.googlesource.com/920991Reviewed-by: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537297}

third_party/WebKit/Source/modules/media_controls/elements/MediaControlTimelineElement.cpp

@@ -273,7 +273,7 @@ void MediaControlTimelineElement::RenderBarSegments() {
       // Draw highlight to show what we have played.
       if (current_position > start_position) {
         SetAfterSegmentPosition(MediaControlSliderElement::Position(
-            start_position, current_position));
+            start_position, current_position - start_position));
       }
 
       // Draw dark grey highlight to show what we have loaded.