gpu: Don't do resource purging if the context is lost.

R=zmo@chromium.org

Bug: 1050220
Change-Id: I50dab36fbf02f228e2660e64982b2f188676d325
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2045203
Auto-Submit: Khushal <khushalsagar@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740059}

gpu/command_buffer/service/shared_context_state.cc

@@ -419,7 +419,8 @@ void SharedContextState::PurgeMemory(
   }
 
   // Ensure the context is current before doing any GPU cleanup.
-  MakeCurrent(nullptr);
+  if (!MakeCurrent(nullptr))
+    return;
 
   switch (memory_pressure_level) {
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE: