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

include/utils/SkThreadPool.h

Index: include/utils/SkThreadPool.h
diff --git a/include/utils/SkThreadPool.h b/include/utils/SkThreadPool.h
index a75bed8be44f538eeb87d3c21658f2de83290618..295b1b4f080004edb111f51570a5beb74b0371b8 100644
--- a/include/utils/SkThreadPool.h
+++ b/include/utils/SkThreadPool.h
@@ -50,6 +50,11 @@ public:
     void add(SkTRunnable<T>*);
 
     /**
+     * Same as add, but adds the runnable as the very next to run rather than enqueueing it.
+     */
+    void addNext(SkTRunnable<T>*);
+
+    /**
      * Block until all added SkRunnables have completed.  Once called, calling add() is undefined.
      */
     void wait();
@@ -66,6 +71,9 @@ public:
         kHalting_State,  // There's no work to do and no thread is busy.  All threads can shut down.
     };
 
+    void addSomewhere(SkTRunnable<T>* r,
+                      void (SkTInternalLList<LinkedRunnable>::*)(LinkedRunnable*));
+
     SkTInternalLList<LinkedRunnable> fQueue;
     SkCondVar                        fReady;
     SkTDArray<SkThread*>             fThreads;
@@ -111,7 +119,8 @@ struct ThreadLocal<void> {
 }  // namespace SkThreadPoolPrivate
 
 template <typename T>
-void SkTThreadPool<T>::add(SkTRunnable<T>* r) {
+void SkTThreadPool<T>::addSomewhere(SkTRunnable<T>* r,
+                                    void (SkTInternalLList<LinkedRunnable>::* f)(LinkedRunnable*)) {
     if (r == NULL) {
         return;
     }
@@ -126,11 +135,21 @@ void SkTThreadPool<T>::add(SkTRunnable<T>* r) {
     linkedRunnable->fRunnable = r;
     fReady.lock();
     SkASSERT(fState != kHalting_State);  // Shouldn't be able to add work when we're halting.
-    fQueue.addToHead(linkedRunnable);
+    (fQueue.*f)(linkedRunnable);
     fReady.signal();
     fReady.unlock();
 }
 
+template <typename T>
+void SkTThreadPool<T>::add(SkTRunnable<T>* r) {
+    this->addSomewhere(r, &SkTInternalLList<LinkedRunnable>::addToTail);
+}
+
+template <typename T>
+void SkTThreadPool<T>::addNext(SkTRunnable<T>* r) {
+    this->addSomewhere(r, &SkTInternalLList<LinkedRunnable>::addToHead);
+}
+
 
 template <typename T>
 void SkTThreadPool<T>::wait() {
@@ -174,7 +193,7 @@ template <typename T>
         // We've got the lock back here, no matter if we ran wait or not.
 
         // The queue is not empty, so we have something to run.  Claim it.
-        LinkedRunnable* r = pool->fQueue.tail();
+        LinkedRunnable* r = pool->fQueue.head();
 
         pool->fQueue.remove(r);