merge options before matrix.update call

- matrix.update() can be expansive (something we should look into),
  so try to call it the least number of times possible.

Author: etpinard

src/traces/splom/index.js

@@ -200,7 +200,7 @@ function plotOne(gd, cd0) {
 
     var visibleDims = trace._visibleDims;
     var visibleLength = cdata.length;
-    var viewOpts = {};
+    var viewOpts = scene.viewOpts = {};
     viewOpts.ranges = new Array(visibleLength);
     viewOpts.domains = new Array(visibleLength);
 
@@ -298,8 +298,8 @@ function plotOne(gd, cd0) {
         }
     }
     else {
-        scene.matrix.update(matrixOpts, null);
-        scene.matrix.update(viewOpts, null);
+        var opts = Lib.extendFlat({}, matrixOpts, viewOpts);
+        scene.matrix.update(opts, null);
         stash.xpx = stash.ypx = null;
     }
 

test/jasmine/tests/splom_test.js

@@ -921,10 +921,10 @@ describe('Test splom drag:', function() {
             var scene = gd._fullLayout._splomScenes[uid];
             // N.B. _drag triggers two updateSubplots call
             // - 1 update and 1 draw call per updateSubplot
-            // - 2 update calls (1 for data, 1 for view opts)
+            // - 1 update calls for data+view opts
             //   during splom plot on mouseup
             // - 1 draw call during splom plot on mouseup
-            expect(scene.matrix.update).toHaveBeenCalledTimes(4);
+            expect(scene.matrix.update).toHaveBeenCalledTimes(3);
             expect(scene.matrix.draw).toHaveBeenCalledTimes(3);
 
             _assertRanges('after drag', [