Ash HUD: Add simple FPS graph.

This CL adds a graph of the scanout time per seconds
reported in the PresentationFeedback.


Screenshot: https://screenshot.googleplex.com/7wZhCV78vtPskdu.png

Bug: 1075612
Change-Id: I16a5320532f35bdc3be4baa6e2bb59bd3db632b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463872
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820879}

diff --git a/ash/hud_display/graph_page_view_base.h b/ash/hud_display/graph_page_view_base.h
index 49cc278..2f8268d8 100644
--- a/ash/hud_display/graph_page_view_base.h
+++ b/ash/hud_display/graph_page_view_base.h

@@ -36,7 +36,7 @@
   // Adds default legend.
   void CreateLegend(const std::vector<Legend::Entry>& entries);
 
-  // Put grid in its dedicated container.
+  // Put grid in its dedicated container. See Grid class for details.
   Grid* CreateGrid(float left,
                    float top,
                    float right,
@@ -44,7 +44,8 @@
                    const base::string16& x_unit,
                    const base::string16& y_unit,
                    int horizontal_points_number,
-                   int horizontal_ticks_interval);
+                   int horizontal_ticks_interval,
+                   float vertical_ticks_interval);
 
  protected:
   void RefreshLegendValues();