Use a per-frame task runner at DeprecatedStorageQuota::quota_host_

V8 should not be executed on per-thread task runner. Use per-frame (per-
execution-context) task runner instead.

Bug: 870606
Change-Id: I353c421901f0ff78966df5d197014f8cb650a985
Reviewed-on: https://chromium-review.googlesource.com/c/1331289Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607172}

third_party/blink/renderer/modules/quota/deprecated_storage_quota.cc

@@ -198,8 +198,11 @@ void DeprecatedStorageQuota::requestQuota(
 mojom::blink::QuotaDispatcherHost& DeprecatedStorageQuota::GetQuotaHost(
     ExecutionContext* execution_context) {
   if (!quota_host_) {
-    ConnectToQuotaDispatcherHost(execution_context,
-                                 mojo::MakeRequest(&quota_host_));
+    ConnectToQuotaDispatcherHost(
+        execution_context,
+        mojo::MakeRequest(&quota_host_,
+                          execution_context->GetTaskRunner(
+                              blink::TaskType::kInternalDefault)));
   }
   return *quota_host_;
 }