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

dm/DMTaskRunner.h

 #ifndef DMTaskRunner_DEFINED
 #define DMTaskRunner_DEFINED
 
 #include "DMGpuSupport.h"
 #include "SkThreadPool.h"
 #include "SkTypes.h"
 
 // TaskRunner runs Tasks on one of two threadpools depending on the need for a GrContextFactory.
 // It's typically a good idea to run fewer GPU threads than CPU threads (go nuts with those).
 
 namespace DM {
 
 class CpuTask;
 class GpuTask;
 
 class TaskRunner : SkNoncopyable {
 public:
     explicit TaskRunner(int cpuThreads, int gpuThreads);
 
     void add(CpuTask* task);
+    void addNext(CpuTask* task);
     void add(GpuTask* task);
     void wait();
 
 private:
     SkTThreadPool<void> fCpu;
     SkTThreadPool<GrContextFactory> fGpu;
 };
 
 }  // namespace DM
 
 #endif  // DMTaskRunner_DEFINED