Add function for calculating grid chip count

This function will be needed to send the chip count to the analytics
server when a game is won.

app/scripts/models/grid.js

@@ -29,6 +29,13 @@ Grid.prototype.checkIfFull = function () {
   });
 };
 
+// Return the total number of chips currently placed on the grid
+Grid.prototype.getChipCount = function () {
+  return this.columns.reduce(function (sum, column) {
+    return sum + column.length;
+  }, 0);
+};
+
 // Reset the grid by removing all placed chips
 Grid.prototype.resetGrid = function () {
   this.columns.forEach(function (column) {

test/grid.spec.js

@@ -69,6 +69,28 @@ describe('grid', function () {
     expect(grid.checkIfFull()).to.be.false;
   });
 
+  it('should count current number of chips when grid is empty', function () {
+    var grid = new Grid({
+      columnCount: 9,
+      rowCount: 8
+    });
+    expect(grid.getChipCount()).to.equal(0);
+  });
+
+  it('should count current number of chips', function () {
+    var grid = new Grid({
+      columnCount: 9,
+      rowCount: 8
+    });
+    var player = new Player({color: 'red', name: 'Bob'});
+    _.times(6, function (c) {
+      _.times(4, function () {
+        grid.placeChip({column: c, chip: new Chip({player: player})});
+      });
+    });
+    expect(grid.getChipCount()).to.equal(24);
+  });
+
   it('should reset', function () {
     var grid = new Grid({
       columnCount: 9,