emit 'plotly_afterplot' once during doAutoMargin redraws

- N.B. consider this a 'temporary' fix until we improve
  the automargin pipeline, see
  #2704
  for more detail.

Author: etpinard

src/plot_api/plot_api.js

@@ -380,7 +380,13 @@ exports.plot = function(gd, data, layout, config) {
 };
 
 function emitAfterPlot(gd) {
-    gd.emit('plotly_afterplot');
+    var fullLayout = gd._fullLayout;
+
+    if(fullLayout._redrawFromAutoMarginCount) {
+        fullLayout._redrawFromAutoMarginCount--;
+    } else {
+        gd.emit('plotly_afterplot');
+    }
 }
 
 exports.setPlotConfig = function setPlotConfig(obj) {

src/plots/plots.js

@@ -1788,8 +1788,15 @@ plots.doAutoMargin = function(gd) {
     gs.h = Math.round(fullLayout.height) - gs.t - gs.b;
 
     // if things changed and we're not already redrawing, trigger a redraw
-    if(!fullLayout._replotting && oldmargins !== '{}' &&
-            oldmargins !== JSON.stringify(fullLayout._size)) {
+    if(!fullLayout._replotting &&
+        oldmargins !== '{}' &&
+        oldmargins !== JSON.stringify(fullLayout._size)
+    ) {
+        if('_redrawFromAutoMarginCount' in fullLayout) {
+            fullLayout._redrawFromAutoMarginCount++;
+        } else {
+            fullLayout._redrawFromAutoMarginCount = 1;
+        }
         return Registry.call('plot', gd);
     }
 };