cc: Fix cleanup path for image decode requests in ImageController.

cc/tiles/image_controller.cc

Index: cc/tiles/image_controller.cc
diff --git a/cc/tiles/image_controller.cc b/cc/tiles/image_controller.cc
index f0d1bb9666c9cde5de93e7879041193d1e74851f..235a3595a05f5b98e1b3c0c08eb274cf6ef58ff4 100644
--- a/cc/tiles/image_controller.cc
+++ b/cc/tiles/image_controller.cc
@@ -77,9 +77,10 @@ void ImageController::StopWorkerTasks() {
     ImageDecodeRequestId id = request_to_complete.first;
     ImageDecodeRequest& request = request_to_complete.second;
 
-    // The task (if one exists) would have run already, so we just need to
-    // complete it.
-    if (request.task)
+    // The task (if one exists) would have run already, we just need to make
+    // sure it was completed. Multiple requests for the same image use the same
+    // task so it could have already been completed.
+    if (request.task && !request.task->HasCompleted())
       request.task->DidComplete();
 
     // Issue the callback, and unref the image immediately. This is so that any
@@ -106,7 +107,9 @@ void ImageController::StopWorkerTasks() {
       // several different image deque requests for the same image.
       if (request.task->state().IsNew())
         request.task->state().DidCancel();
-      request.task->DidComplete();
+
+      if (!request.task->HasCompleted())
+        request.task->DidComplete();
     }
     // Run the callback and unref the image.
     request.callback.Run(id);
@@ -120,7 +123,10 @@ void ImageController::SetImageDecodeCache(ImageDecodeCache* cache) {
     SetPredecodeImages(std::vector<DrawImage>(),
                        ImageDecodeCache::TracingInfo());
     StopWorkerTasks();
+  } else if (cache_ && cache_ != cache) {

[vmpstr, 2017/02/17 21:15:13]

Don't do this... We specifically talked about it and we only support setting
non-null to null or vice versa

[Khushal, 2017/02/17 21:17:35]

Should I add a DCHECK for that then? Makes it obvious for someone reading this
too.

[vmpstr, 2017/02/17 21:22:09]

Yeah I'm not sure why we don't have a DCHECK, there must have been a reason.
Actually, I think what you have here is fine. Can you just make sure to call
SetPredecodeImages as well (just combine the two if statements)

+    StopWorkerTasks();
   }
+
   cache_ = cache;
 }