Logging to ensure that non-offscreen surfaces are destroyed as expected

We're hitting scenarios where it appears that we may be creating an
EGL window surface for a given window before destroying the previous.
This leads to errors on Android, and shouldn't be possible. We're
suspecting that someone may be taking a reference on the glSurface,
extending the lifetime beyond the expected range. This CL adds logging
to catch this scenario.

Bug: 787086
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I31bb0c55fb393a0719486f32f885273ee81ab9f8
Reviewed-on: https://chromium-review.googlesource.com/802186
Commit-Queue: Eric Karl <ericrk@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522293}

gpu/command_buffer/service/gles2_cmd_decoder.cc

@@ -5019,6 +5019,9 @@ void GLES2DecoderImpl::Destroy(bool have_context) {
     transform_feedback_manager_.reset();
   }
 
+  // Record this value before resetting the frame buffer below.
+  bool is_offscreen = !!offscreen_target_frame_buffer_;
+
   offscreen_target_frame_buffer_.reset();
   offscreen_target_color_texture_.reset();
   offscreen_target_color_render_buffer_.reset();
@@ -5048,6 +5051,13 @@ void GLES2DecoderImpl::Destroy(bool have_context) {
     group_ = NULL;
   }
 
+  // If this is not an offscreen surface then it shouldn't be shared and we
+  // should have the only remaining ref. Logging to debug crbug.com/787086
+  if (!is_offscreen && surface_ && !surface_->HasOneRef()) {
+    LOG(ERROR) << "crbug.com/787086: Decoder is not the sole owner of "
+                  "|surface_| at destruction time";
+  }
+
   // Destroy the surface before the context, some surface destructors make GL
   // calls.
   surface_ = nullptr;