Use per-frame TaskRunner instead of thread's default in DataConsumerHandle

content/child/shared_memory_data_consumer_handle.cc

Index: content/child/shared_memory_data_consumer_handle.cc
diff --git a/content/child/shared_memory_data_consumer_handle.cc b/content/child/shared_memory_data_consumer_handle.cc
index 3c9b7a26ff8e65e81374fbc3a9524c8323ac5d96..ba5e2cec2973ecb7853a545e46583a551cccd5b1 100644
--- a/content/child/shared_memory_data_consumer_handle.cc
+++ b/content/child/shared_memory_data_consumer_handle.cc
@@ -15,6 +15,7 @@
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "components/scheduler/child/web_task_runner_impl.h"
 #include "content/public/child/fixed_received_data.h"
 
 namespace content {
@@ -119,7 +120,15 @@ class SharedMemoryDataConsumerHandle::Context final
     lock_.AssertAcquired();
     DCHECK(!notification_task_runner_);
     DCHECK(!client_);
-    notification_task_runner_ = base::ThreadTaskRunnerHandle::Get();
+
+    blink::WebTaskRunner* task_runner =
+        client ? client->getTaskRunner() : nullptr;
+    if (task_runner) {
+      notification_task_runner_ =
+          scheduler::WebTaskRunnerImpl::GetBaseTaskRunner(*task_runner);

[kinuko, 2016/07/28 15:41:31]

Per Sami's comment this would be a tentative solution but this code makes me
feel uneasy :(  There doesn't seem enough guarantee that this is going to be
always safe.

Does it make sense to instead use WebTaskRunner for notification_task_runner_
for now?  (For null-client case could we use
Platform::current()->currentThread()->getWebTaskRunner()?)

Or I think we need some comment at least to explicitly note that this should be
safe and will be gone soon.

(Or if we're landing the scheduler migration patch first we won't need this
hack, I assume)

+    } else {
+      notification_task_runner_ = base::ThreadTaskRunnerHandle::Get();
+    }
     client_ = client;
     if (client && !(IsEmpty() && result() == Ok)) {
       // We cannot notify synchronously because the user doesn't have the reader