[added] warningPrefix option

warningPrefix allows one to specify an optional prefix to be added
to the failure message.

Author: matt-royal

lib/__tests__/index-test.js

@@ -637,3 +637,25 @@ describe('exclusions', () => {
     });
   });
 });
+
+describe('warningPrefix', () => {
+  var createElement = React.createElement;
+
+  let warningPrefix = 'react-a11y ERROR:';
+  before(() => {
+    a11y(React, { warningPrefix });
+  });
+
+  after(() => {
+    React.createElement = createElement;
+  });
+
+  it('adds the prefix to each warning message', () => {
+    expectWarning(warningPrefix + assertions.tags.img.MISSING_ALT.msg, () => {
+      <div>
+        <img id="foo" src="foo.jpg"/>
+        <img id="bar" src="foo.jpg"/>
+      </div>;
+    });
+  });
+});

lib/index.js

@@ -128,6 +128,7 @@ var logWarning = (component, failureInfo, options) => {
 
 var handleFailure = (options, reactEl, type, props, failureMsg) => {
   var includeSrcNode = options && !!options.includeSrcNode;
+  var warningPrefix = (options && options.warningPrefix) || '';
   var reactComponent = reactEl._owner;
 
   // If a Component instance, use the component's name,
@@ -138,7 +139,7 @@ var handleFailure = (options, reactEl, type, props, failureMsg) => {
   var failureInfo = {
     'tagName': name ,
     'id': props.id,
-    'msg': failureMsg
+    'msg': warningPrefix + failureMsg
   };
 
   var notifyOpts = {