Fix ImageUploadTaskImpl with null dependencies.

cc/tiles/gpu_image_decode_controller.cc

Index: cc/tiles/gpu_image_decode_controller.cc
diff --git a/cc/tiles/gpu_image_decode_controller.cc b/cc/tiles/gpu_image_decode_controller.cc
index 04a25a33fe87c1acaf02dadc9db3672dcd1456bf..2205a2752e0d27243b7f201cd629d1a6575f648c 100644
--- a/cc/tiles/gpu_image_decode_controller.cc
+++ b/cc/tiles/gpu_image_decode_controller.cc
@@ -110,7 +110,10 @@ class ImageUploadTaskImpl : public TileTask {
         image_ref_(draw_image.image()),
         source_prepare_tiles_id_(source_prepare_tiles_id) {
     DCHECK(!SkipImage(draw_image));
-    dependencies_.push_back(std::move(decode_dependency));
+    // If an image is already decoded and locked, we will not generate a
+    // decode task.
+    if (decode_dependency)

[prashant.n, 2016/04/21 21:57:51]

Add DCHECK(decode_dependency) here.

[ericrk, 2016/04/21 23:06:39]

We can have legitimate cases where an upload task doesn't need a decode
dependency - in cases where we just need to upload data, but it was already
decoded.

+      dependencies_.push_back(std::move(decode_dependency));
   }
 
   // Override from Task: