[Plot] Fix refactoring issues

Fix issues related to refactoring of view-level
to subplot-level behavior, such that previous
functionality is restored. This refactoring
supports introduction of a stacked-plot mode,
for WTD-625.

platform/features/plot/src/modes/PlotModeOptions.js

@@ -1,7 +1,7 @@
 /*global define*/
 
 define(
-    [],
+    ["./PlotOverlayMode"],
     function (PlotOverlayMode, PlotStackedMode) {
         "use strict";
 
@@ -15,7 +15,7 @@ define(
                 key: "overlaid",
                 name: "Overlaid",
                 glyph: "6",
-                factory: PlotStackedMode
+                factory: PlotOverlayMode
             };
 
         function PlotModeOptions(telemetryObjects) {

platform/features/plot/src/modes/PlotOverlayMode.js

@@ -22,7 +22,7 @@ define(
                 // Track the domain offset, used to bias domain values
                 // to minimize loss of precision when converted to 32-bit
                 // floating point values for display.
-                domainOffset = prepared.getDomainOffset();
+                subplot.setDomainOffset(prepared.getDomainOffset());
 
                 // Draw the buffers. Select color by index.
                 subplot.getDrawingObject().lines = prepared.getBuffers().map(function (buf, i) {