Filter out jitcode from C++ only call tree; Resolves firefox-devtools…

…#285 (firefox-devtools#292)

* Filter out jitcode from C++ only call tree

* Address review comments

src/content/profile-data.js

@@ -133,11 +133,24 @@ export function defaultThreadOrder(threads: Thread[]) {
 }
 
 export function filterThreadByImplementation(thread: Thread, implementation: string): Thread {
-  const { funcTable } = thread;
+  const { funcTable, stringTable } = thread;
 
   switch (implementation) {
     case 'cpp':
-      return _filterThreadByFunc(thread, funcIndex => !funcTable.isJS[funcIndex]);
+      return _filterThreadByFunc(thread, funcIndex => {
+        // Return quickly if this is a JS frame.
+        if (funcTable.isJS[funcIndex]) {
+          return false;
+        }
+        // Regular C++ functions are associated with a resource that describes the
+        // shared library that these C++ functions were loaded from. Jitcode is not
+        // loaded from shared libraries but instead generated at runtime, so Jitcode
+        // frames are not associated with a shared library and thus have no resource
+        const locationString = stringTable.getString(funcTable.name[funcIndex]);
+        const isProbablyJitCode =
+          funcTable.resource[funcIndex] === -1 && locationString.startsWith('0x');
+        return !isProbablyJitCode;
+      });
     case 'js':
       return _filterThreadByFunc(thread, funcIndex => funcTable.isJS[funcIndex]);
   }