progressView 单例 解决多个progress的bug code review by 高强

@@ -164,6 +164,16 @@ static float kprogressViewRadius = 2.0f;
     }
 }
 
+-(YHWebViewProgressView *)progressView
+{
+    static YHWebViewProgressView *sharedProgressViewInstance = nil;
+    static dispatch_once_t predicate;
+    dispatch_once(&predicate, ^{
+        sharedProgressViewInstance = [[YHWebViewProgressView alloc] init];
+    });
+    return sharedProgressViewInstance;
+}
+
 - (NSMutableArray *)autoSchemes
 {
     if (!_autoSchemes) {