Fixed GetGpuBlockedTimeSinceLastSwap crash

Some examples and tests create InProcessCommandBuffer without
GpuChannelManagerDelegate. Some of them would crash trying to report new
GpuBlockedTimeBetweenSwaps metric because of it. This CL fixes crash.

Fixed: 1022412
Change-Id: I61a0a8a663d91bcf608ec2992d01b9d0752de8c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1903841Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713512}

gpu/ipc/in_process_command_buffer.cc

@@ -1773,6 +1773,11 @@ viz::GpuVSyncCallback InProcessCommandBuffer::GetGpuVSyncCallback() {
 }
 
 base::TimeDelta InProcessCommandBuffer::GetGpuBlockedTimeSinceLastSwap() {
+  // Some examples and tests create InProcessCommandBuffer without
+  // GpuChannelManagerDelegate.
+  if (!gpu_channel_manager_delegate_)
+    return base::TimeDelta::Min();
+
   return gpu_channel_manager_delegate_->GetGpuScheduler()
       ->TakeTotalBlockingTime();
 }