DM: Push GPU-parent child tasks to the front of the queue.

dm/DMTaskRunner.cpp

 #include "DMTaskRunner.h"
 #include "DMTask.h"
 
 namespace DM {
 
 TaskRunner::TaskRunner(int cpuThreads, int gpuThreads) : fCpu(cpuThreads), fGpu(gpuThreads) {}
 
 void TaskRunner::add(CpuTask* task) { fCpu.add(task); }
-
+void TaskRunner::addNext(CpuTask* task) { fCpu.addNext(task); }
 void TaskRunner::add(GpuTask* task) { fGpu.add(task); }
 
 void TaskRunner::wait() {
     // These wait calls block until each threadpool is done.  We don't allow
     // spawning new child GPU tasks, so we can wait for that first knowing
     // we'll never try to add to it later.  Same can't be said of the CPU pool:
     // both CPU and GPU tasks can spawn off new CPU work, so we wait for that last.
     fGpu.wait();
     fCpu.wait();
 }
 
 }  // namespace DM