Fix up Perf a bit better for 0.13

_mountImageIntoNode moved into ReactMount and wasn't being counted where it was supposed to be. In addition, all DOM elements are now wrapped in a composite wrapper but for the perf tools we want to skip over those or else we'll double-count (at least with the current accounting -- and that's effectively what we did before so this brings us back up to parity).

Fixes #3407.

Test Plan:
Used the jsbin from #3407 and saw similar output from this branch and 0.12:

![image](https://cloud.githubusercontent.com/assets/6820/6649816/4d7202e0-c9b2-11e4-9364-e1b50c96b55b.png)

src/test/ReactDefaultPerf.js

@@ -163,8 +163,8 @@ var ReactDefaultPerf = {
           ReactDefaultPerf._allMeasurements.length - 1
         ].totalTime = performanceNow() - start;
         return rv;
-      } else if (moduleName === 'ReactDOMIDOperations' ||
-        moduleName === 'ReactComponentBrowserEnvironment') {
+      } else if (fnName === '_mountImageIntoNode' ||
+          moduleName === 'ReactDOMIDOperations') {
         start = performanceNow();
         rv = func.apply(this, args);
         totalTime = performanceNow() - start;
@@ -210,6 +210,10 @@ var ReactDefaultPerf = {
         fnName === 'updateComponent' || // TODO: receiveComponent()?
         fnName === '_renderValidatedComponent')) {
 
+        if (typeof this._currentElement.type === 'string') {
+          return func.apply(this, args);
+        }
+
         var rootNodeID = fnName === 'mountComponent' ?
           args[0] :
           this._rootNodeID;
@@ -243,9 +247,7 @@ var ReactDefaultPerf = {
         }
 
         entry.displayNames[rootNodeID] = {
-          current: typeof this._currentElement.type === 'string' ?
-            this._currentElement.type :
-            this.getName(),
+          current: this.getName(),
           owner: this._currentElement._owner ?
             this._currentElement._owner.getName() :
             '<root>'