Use RenderFrame::GetTaskRunner in content/renderer/pepper/.

Presubmit complains about using ThreadTaskRunnerHandle in the renderer
saying that we should use GetTaskRunner instead.

** Presubmit Warnings **
base::ThreadTaskRunnerHandle::Get() and base::SequencedTaskRunnerHandle::Get() are deprecated in renderer; please use RenderFrame::GetTaskRunner for production code and blink::scheduler::Get*TaskRunnerForTesting for tests. Please reach out to scheduler-dev@ if you have any questions.
  content/renderer/pepper/plugin_power_saver_helper.cc:87

R=raymes@chromium.org

Bug: 953861
Change-Id: I9b5716d03eb8805e9a57e70dca37a21290fe59cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1618146Reviewed-by: Raymes Khoury <raymes@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Auto-Submit: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662241}

content/renderer/pepper/plugin_power_saver_helper.cc

@@ -84,8 +84,9 @@ void PluginPowerSaverHelper::OnUpdatePluginContentOriginWhitelist(
     if (origin_whitelist.count(it->content_origin)) {
       // Because the unthrottle callback may register another peripheral plugin
       // and invalidate our iterator, we cannot run it synchronously.
-      base::ThreadTaskRunnerHandle::Get()->PostTask(
-          FROM_HERE, std::move(it->unthrottle_callback));
+      render_frame()
+          ->GetTaskRunner(blink::TaskType::kInternalDefault)
+          ->PostTask(FROM_HERE, std::move(it->unthrottle_callback));
       it = peripheral_plugins_.erase(it);
     } else {
       ++it;