webrtc-internals: increase the maximum precision of the graphs

increases the maximum precision of the graphs drawn to 3
since we can have values like jitter or roundtrip time which are
measured in seconds but can have millisecond values

BUG=chromium:678292

Change-Id: Ibcde153a518d65d1beae2cfb137f39da602b131c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2382837Reviewed-by: Henrik Boström <hbos@chromium.org>
Reviewed-by: Tommi <tommi@chromium.org>
Commit-Queue: Tommi <tommi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803128}

content/browser/resources/media/timeline_graph_view.js

@@ -28,7 +28,7 @@ var TimelineGraphView = (function() {
   var TEXT_COLOR = '#000';
   var BACKGROUND_COLOR = '#FFF';
 
-  var MAX_DECIMAL_PRECISION = 2;
+  var MAX_DECIMAL_PRECISION = 3;
   /**
    * @constructor
    */