gpu: Fix some context lost marking glitches+leaks and add UMA stats

gpu/command_buffer/service/context_group.cc

Index: gpu/command_buffer/service/context_group.cc
diff --git a/gpu/command_buffer/service/context_group.cc b/gpu/command_buffer/service/context_group.cc
index 17871b97f4d743810fca52395189c5301b391ebc..d2667f072e1953a7a1042de6f80351d3a846a8c3 100644
--- a/gpu/command_buffer/service/context_group.cc
+++ b/gpu/command_buffer/service/context_group.cc
@@ -360,10 +360,10 @@ uint32 ContextGroup::GetMemRepresented() const {
   return total;
 }
 
-void ContextGroup::LoseContexts(GLenum reset_status) {
+void ContextGroup::LoseContexts(error::ContextLostReason reason) {
   for (size_t ii = 0; ii < decoders_.size(); ++ii) {
     if (decoders_[ii].get()) {
-      decoders_[ii]->LoseContext(reset_status);
+      decoders_[ii]->MarkContextLost(reason);
     }
   }
 }