Proxy global PDFJS.verbosity to properly configure shared/util.

src/doc_helper.js

@@ -27,6 +27,16 @@ function PDFJS() {
   // Mock class constructor. See src/display/api.js.
 }
 
+/**
+ * Controls the logging level.
+ * The constants from PDFJS.VERBOSITY_LEVELS should be used:
+ * - errors
+ * - warnings [default]
+ * - infos
+ * @var {number}
+ */
+PDFJS.verbosity = PDFJS.VERBOSITY_LEVELS.warnings;
+
 /**
  * Represents the eventual result of an asynchronous operation.
  * @external Promise