MultiPictureDraw is taskgroup aware.

src/core/SkTaskGroup.cpp

 #include "SkTaskGroup.h"
 
 #include "SkCondVar.h"
+#include "SkRunnable.h"
 #include "SkTDArray.h"
 #include "SkThread.h"
 #include "SkThreadUtils.h"
 
 #if defined(SK_BUILD_FOR_WIN32)
     static inline int num_cores() {
         SYSTEM_INFO sysinfo;
         GetSystemInfo(&sysinfo);
         return sysinfo.dwNumberOfProcessors;
     }
@@ skipping 137 matching lines @@
 SkTaskGroup::Enabler::~Enabler() {
     SkDELETE(ThreadPool::gGlobal);
 }
 
 SkTaskGroup::SkTaskGroup() : fPending(0) {}
 
 void SkTaskGroup::add(SkRunnable* task)             { ThreadPool::Add(task, &fPending); }
 void SkTaskGroup::add(void (*fn)(void*), void* arg) { ThreadPool::Add(fn, arg, &fPending); }
 void SkTaskGroup::wait()                            { ThreadPool::Wait(&fPending); }