Add execution time elapsed to JsApiReporter

Since this information is desired in ConsoleReporter, HtmlReporter,
and now JsApiReporter, the executionTime is passed through in
jasmineDone from Env instead of making each reporter compute it.

Fixes #30, [Finishes #45659879]

src/core/JsApiReporter.js

@@ -11,8 +11,11 @@ getJasmineRequireObj().JsApiReporter = function() {
       status = 'started';
     };
 
-    this.jasmineDone = function() {
+    var executionTime;
+
+    this.jasmineDone = function(options) {
       this.finished = true;
+      executionTime = options.executionTime;
       status = 'done';
     };
 
@@ -53,6 +56,10 @@ getJasmineRequireObj().JsApiReporter = function() {
       return specs;
     };
 
+    this.executionTime = function() {
+      return executionTime;
+    };
+
   }
 
   return JsApiReporter;