hud_display: Clean up size calculations and code aesthetics

Bug: none
Test: manual
Change-Id: Ia1a58c919c9006f792482ed171643313a424806b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3044230
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#904505}

diff --git a/ash/hud_display/graph.h b/ash/hud_display/graph.h
index 39538d0..b4283af 100644
--- a/ash/hud_display/graph.h
+++ b/ash/hud_display/graph.h

@@ -25,7 +25,7 @@
   // Graph screen size (that is used in Layout()) should match (ring buffer
   // size - 1) to prevent scaling, because RingBuffer always keeps one element
   // unused.
-  using Data = base::RingBuffer<float, kDefaultGraphWidth + 1>;
+  using Data = base::RingBuffer<float, kHUDGraphWidth + 1>;
 
   enum class Baseline {
     BASELINE_BOTTOM,  // Positive values will be drawn from the bottom border