Adding Sinon extern for getCalls().
This is needed to be able to assert that a stub/spy was called X number of times.
See the 1.17.7 documentation which lists `spy.getCalls()` as an API:
@@ -317,6 +317,11 @@ SinonSpy.prototype.invokeCallback = function(args) {};
*/
SinonSpy.prototype.getCall = function(n) {};
+/**
+ * @return {!Array<!SinonSpyCall>}
+ */
+SinonSpy.prototype.getCalls = function() {};
+
SinonSpy.prototype.reset = function() {};
/**
