Bug 1177293 - Don't overcount samples when flattening recursion. r=jsantell

browser/devtools/performance/modules/logic/tree-model.js

@@ -219,7 +219,8 @@ ThreadNode.prototype = {
 
         // If we shouldn't flatten the current frame into the previous one, advance a
         // level in the call tree.
-        if (!flattenRecursion || frameKey !== prevFrameKey) {
+        let shouldFlatten = flattenRecursion && frameKey === prevFrameKey;
+        if (!shouldFlatten) {
           calls = prevCalls;
         }
 
@@ -233,7 +234,11 @@ ThreadNode.prototype = {
                                         sampleTime, stringTable);
           }
         }
-        frameNode.samples++;
+
+        // Don't overcount flattened recursive frames.
+        if (!shouldFlatten) {
+          frameNode.samples++;
+        }
 
         prevFrameKey = frameKey;
         prevCalls = frameNode.calls;