Added JSONKit support

Summary:
React Native will now use JSONKit if it's already available in the project, otherwise it will fall back to using NSJSONSerialization as before. This provides a small performance boost to JSON parsing in some cases.

Examples/UIExplorer/UIExplorerUnitTests/RCTJSONTests.m

@@ -0,0 +1,81 @@
+/**
+ * The examples provided by Facebook are for non-commercial testing and
+ * evaluation purposes only.
+ *
+ * Facebook reserves all rights not expressly granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON INFRINGEMENT. IN NO EVENT SHALL
+ * FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#import <XCTest/XCTest.h>
+#import "RCTUtils.h"
+
+@interface RCTJSONTests : XCTestCase
+
+@end
+
+@implementation RCTJSONTests
+
+- (void)testEncodingObject
+{
+  NSDictionary *obj = @{@"foo": @"bar"};
+  NSString *json = @"{\"foo\":\"bar\"}";
+  XCTAssertEqualObjects(json, RCTJSONStringify(obj, NULL));
+}
+
+- (void)testEncodingArray
+{
+  NSArray *array = @[@"foo", @"bar"];
+  NSString *json = @"[\"foo\",\"bar\"]";
+  XCTAssertEqualObjects(json, RCTJSONStringify(array, NULL));
+}
+
+- (void)testEncodingString
+{
+  NSString *text = @"Hello\nWorld";
+  NSString *json = @"\"Hello\\nWorld\"";
+  XCTAssertEqualObjects(json, RCTJSONStringify(text, NULL));
+}
+
+- (void)testDecodingObject
+{
+  NSDictionary *obj = @{@"foo": @"bar"};
+  NSString *json = @"{\"foo\":\"bar\"}";
+  XCTAssertEqualObjects(obj, RCTJSONParse(json, NULL));
+}
+
+- (void)testDecodingArray
+{
+  NSArray *array = @[@"foo", @"bar"];
+  NSString *json = @"[\"foo\",\"bar\"]";
+  XCTAssertEqualObjects(array, RCTJSONParse(json, NULL));
+}
+
+- (void)testDecodingString
+{
+  NSString *text = @"Hello\nWorld";
+  NSString *json = @"\"Hello\\nWorld\"";
+  XCTAssertEqualObjects(text, RCTJSONParse(json, NULL));
+}
+
+- (void)testDecodingMutableArray
+{
+  NSString *json = @"[1,2,3]";
+  NSMutableArray *array = RCTJSONParseMutable(json, NULL);
+  XCTAssertNoThrow([array addObject:@4]);
+  XCTAssertEqualObjects(array, (@[@1, @2, @3, @4]));
+}
+
+- (void)testLeadingWhitespace
+{
+  NSDictionary *obj = @{@"foo": @"bar"};
+  NSString *json = @" \r\n\t{\"foo\":\"bar\"}";
+  XCTAssertEqualObjects(obj, RCTJSONParse(json, NULL));
+}
+
+@end