added _(...).countBy defs

lodash/lodash-tests.ts

@@ -284,6 +284,10 @@ result = <_.Dictionary<number>>_.countBy([4.3, 6.1, 6.4], function(num) { return
 result = <_.Dictionary<number>>_.countBy([4.3, 6.1, 6.4], function(num) { return this.floor(num); }, Math);
 result = <_.Dictionary<number>>_.countBy(['one', 'two', 'three'], 'length');
 
+	result = <_.LoDashWrapper<_.Dictionary<number>>>_([4.3, 6.1, 6.4]).countBy(function(num) { return Math.floor(num); });
+	result = <_.LoDashWrapper<_.Dictionary<number>>>_([4.3, 6.1, 6.4]).countBy(function(num) { return this.floor(num); }, Math);
+	result = <_.LoDashWrapper<_.Dictionary<number>>>_(['one', 'two', 'three']).countBy('length');
+
 result = <boolean>_.every([true, 1, null, 'yes'], Boolean);
 result = <boolean>_.every(stoogesAges, 'age');
 result = <boolean>_.every(stoogesAges, { 'age': 50 });

lodash/lodash.d.ts

@@ -1099,13 +1099,30 @@ declare module _ {
 
 	/**
 	* @see _.countBy
-	* @param iterator Function name
+	* @param callback Function name
 	**/
 	export function countBy<T>(
 		collection: Collection<T>,
 		callback: string,
 		thisArg?: any): Dictionary<number>;
 
+		interface LoDashWrapper<T> {
+			/**
+			* @see _.countBy
+			**/
+			countBy<T>(
+				callback?: ListIterator<T, any>,
+				thisArg?: any): LoDashWrapper<Dictionary<number>>;
+
+			/**
+			* @see _.countBy
+			* @param callback Function name
+			**/
+			countBy<T>(
+				callback: string,
+				thisArg?: any): LoDashWrapper<Dictionary<number>>;
+		}
+
 	/**
 	* Checks if the given callback returns truey value for all elements of a collection. 
 	* The callback is bound to thisArg and invoked with three arguments; (value, index|key,