migrate skpdiff to tools

tools/skpdiff/diff_viewer.js

 angular.module('diff_viewer', []).
 config(['$routeProvider', function($routeProvider) {
     // Show the list of differences by default
     $routeProvider.
     otherwise({ templateUrl: '/diff_list.html', controller: DiffListController});
 }]).
 directive('swapImg', function() {
     // Custom directive for showing an image that gets swapped my mouseover.
     return {
         restrict: 'E', // The directive can be used as an element name
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     // Called by the sort buttons to adjust the metric used for sorting
     $scope.setSortIndex = function(idx) {
         $scope.sortIndex = idx;
     };
 
     // A predicate for pulling out the number used for sorting
     $scope.sortingDiffer = function(record) {
         return record.diffs[$scope.sortIndex].result;
     };
 }