EstablishGpuChannel directly if in the task runner thread

This follows up:
https://chromium-review.googlesource.com/c/chromium/src/+/1125518/22/content/browser/gpu/gpu_client_impl.cc#70

BUG=857217

Change-Id: I4139661d39744bed3aab9ccdda72fc2976739472
Reviewed-on: https://chromium-review.googlesource.com/1136221
Commit-Queue: Xing Xu <xing.xu@intel.com>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575196}

content/browser/gpu/gpu_client_impl.cc

@@ -67,11 +67,14 @@ void GpuClientImpl::OnError(ErrorReason reason) {
 }
 
 void GpuClientImpl::PreEstablishGpuChannel() {
-  DCHECK(!task_runner_->RunsTasksInCurrentSequence());
-  task_runner_->PostTask(
-      FROM_HERE,
-      base::BindOnce(&GpuClientImpl::EstablishGpuChannel,
-                     base::Unretained(this), EstablishGpuChannelCallback()));
+  if (task_runner_->RunsTasksInCurrentSequence()) {
+    EstablishGpuChannel(EstablishGpuChannelCallback());
+  } else {
+    task_runner_->PostTask(
+        FROM_HERE,
+        base::BindOnce(&GpuClientImpl::EstablishGpuChannel,
+                       base::Unretained(this), EstablishGpuChannelCallback()));
+  }
 }
 
 void GpuClientImpl::SetConnectionErrorHandler(