cc: Add image decode queue functionality to image manager.

cc/tiles/gpu_image_decode_cache_unittest.cc

Index: cc/tiles/gpu_image_decode_cache_unittest.cc
diff --git a/cc/tiles/gpu_image_decode_cache_unittest.cc b/cc/tiles/gpu_image_decode_cache_unittest.cc
index 072dfd91d9f2d7355c433f0b5caae8bcec893a97..34d2b29005fe9c743c563603d4a2e556daa4590c 100644
--- a/cc/tiles/gpu_image_decode_cache_unittest.cc
+++ b/cc/tiles/gpu_image_decode_cache_unittest.cc
@@ -497,6 +497,7 @@ TEST(GpuImageDecodeCacheTest, GetTaskForImageCanceledWhileReffedGetsNewTask) {
   EXPECT_TRUE(need_unref);
   EXPECT_TRUE(task);
 
+  ASSERT_GT(task->dependencies().size(), 0u);
   TestTileTaskRunner::ProcessTask(task->dependencies()[0].get());
 
   scoped_refptr<TileTask> another_task;
@@ -509,6 +510,10 @@ TEST(GpuImageDecodeCacheTest, GetTaskForImageCanceledWhileReffedGetsNewTask) {
   TestTileTaskRunner::CancelTask(task.get());
   TestTileTaskRunner::CompleteTask(task.get());
 
+  // 2 Unrefs, so that the decode is unlocked as well.
+  cache.UnrefImage(draw_image);
+  cache.UnrefImage(draw_image);
+
   // Note that here, everything is reffed, but a new task is created. This is
   // possible with repeated schedule/cancel operations.
   scoped_refptr<TileTask> third_task;
@@ -518,12 +523,11 @@ TEST(GpuImageDecodeCacheTest, GetTaskForImageCanceledWhileReffedGetsNewTask) {
   EXPECT_TRUE(third_task);
   EXPECT_FALSE(third_task.get() == task.get());
 
+  ASSERT_GT(third_task->dependencies().size(), 0u);
   TestTileTaskRunner::ProcessTask(third_task->dependencies()[0].get());
   TestTileTaskRunner::ProcessTask(third_task.get());
 
-  // 3 Unrefs!
-  cache.UnrefImage(draw_image);
-  cache.UnrefImage(draw_image);
+  // Unref!
   cache.UnrefImage(draw_image);
 }