Add log API to Blob and XMLHttpRequest

src/polyfill/Blob.js

     return this._ref
   }
 
+  static setLog(level:number) {
+    if(number === -1)
+      log.disable()
+    else
+      log.level(level)
+  }
+
   /**
    * RNFetchBlob Blob polyfill, create a Blob directly from file path, BASE64
    * encoded data, and string. The conversion is done implicitly according to

src/polyfill/XMLHttpRequest.js

     return DONE
   }
 
+  static setLog(level:number) {
+    if(number === -1)
+      log.disable()
+    else
+      log.level(level)
+  }
+
   static addBinaryContentType(substr:string) {
     for(let i in XMLHttpRequest.binaryContentTypes) {
       if(new RegExp(substr,'i').test(XMLHttpRequest.binaryContentTypes[i])) {

src/utils/log.js

   }
 
   level(val:number) {
+    this._isEnable = true
     this._level = val
   }