Added Destroy() functions for GPUTimer and GPUTracer/GPUTrace.

BUG=467202
TEST=Shut down during gpu.device trace has no warnings.

Review URL: https://codereview.chromium.org/1018773002

Cr-Commit-Position: refs/heads/master@{#322304}
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 0886768..a9cb5fe 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -3755,6 +3755,10 @@
   // by the context group.
   async_pixel_transfer_manager_.reset();
 
+  // Destroy the GPU Tracer which may own some in process GPU Timings.
+  gpu_tracer_->Destroy(have_context);
+  gpu_tracer_ = NULL;
+
   if (group_.get()) {
     framebuffer_manager()->RemoveObserver(this);
     group_->Destroy(this, have_context);