Revert of SkThreadPool ~~> SkTaskGroup

dm/DMTask.h

 #ifndef DMTask_DEFINED
 #define DMTask_DEFINED
 
+#include "DMReporter.h"
 #include "DMGpuSupport.h"
-#include "DMReporter.h"
 #include "SkRunnable.h"
-#include "SkTaskGroup.h"
 #include "SkTime.h"
 
 // DM will run() these tasks on one of two threadpools.
 // Subclasses can call fail() to mark this task as failed, or make any number of spawnChild() calls
 // to kick off dependent tasks.
 //
 // Tasks delete themselves when run.
 
 namespace DM {
 
@@ skipping 12 matching lines @@
 
 protected:
     Task(Reporter* reporter, TaskRunner* taskRunner);
     Task(const Task& parent);
     virtual ~Task();
 
     void start();
     void fail(const char* msg = NULL);
     void finish();
 
-    void reallySpawnChild(CpuTask* task);  // For now we don't allow GPU child tasks.
+    void spawnChildNext(CpuTask* task);  // For now we don't allow GPU child tasks.
 
 private:
     Reporter* fReporter;      // Unowned.
     TaskRunner* fTaskRunner;  // Unowned.
     int fDepth;
     SkMSec fStart;
 };
 
 class CpuTask : public Task, public SkRunnable {
 public:
     CpuTask(Reporter* reporter, TaskRunner* taskRunner);
     CpuTask(const Task& parent);
     virtual ~CpuTask() {}
 
     void run() SK_OVERRIDE;
     virtual void draw() = 0;
 
     void spawnChild(CpuTask* task);
 };
 
-class GpuTask : public Task {
+class GpuTask : public Task, public SkTRunnable<GrContextFactory> {
  public:
     GpuTask(Reporter* reporter, TaskRunner* taskRunner);
     virtual ~GpuTask() {}
 
-    void run(GrContextFactory*);
+    void run(GrContextFactory&) SK_OVERRIDE;
     virtual void draw(GrContextFactory*) = 0;
 
     void spawnChild(CpuTask* task);
 };
 
 }  // namespace DM
 
 #endif  // DMTask_DEFINED