SkThreadPool: tweak two little things that have been annoying me
 1) it's pretty annoying that SkThreadPool doesn't include SkRunnable for us;
 2) add wait() so we don't have to keep using SkAutoTDelete/free() to wait for completion.

BUG=
R=scroggo@google.com, reed@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/26470005

git-svn-id: http://skia.googlecode.com/svn/trunk@11711 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/utils/SkThreadPool.h b/include/utils/SkThreadPool.h
index 9865703..6cb8b52 100644
--- a/include/utils/SkThreadPool.h
+++ b/include/utils/SkThreadPool.h
@@ -9,10 +9,10 @@
 #define SkThreadPool_DEFINED
 
 #include "SkCondVar.h"
+#include "SkRunnable.h"
 #include "SkTDArray.h"
 #include "SkTInternalLList.h"
 
-class SkRunnable;
 class SkThread;
 
 class SkThreadPool {
@@ -31,6 +31,11 @@
      */
     void add(SkRunnable*);
 
+    /**
+     * Block until all added SkRunnables have completed.  Once called, calling add() is undefined.
+     */
+    void wait();
+
  private:
     struct LinkedRunnable {
         // Unowned pointer.