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

ui/gl/gpu_timing.cc

Index: ui/gl/gpu_timing.cc
diff --git a/ui/gl/gpu_timing.cc b/ui/gl/gpu_timing.cc
index a84d3f76497bffe19efabfe78a30ecaab3a2f35c..ee9049093471973237c85fada92bd5f66300fca4 100644
--- a/ui/gl/gpu_timing.cc
+++ b/ui/gl/gpu_timing.cc
@@ -44,7 +44,16 @@ uint32_t GPUTiming::GetDisjointCount() {
 }
 
 GPUTimer::~GPUTimer() {
-  glDeleteQueries(2, queries_);
+  // Destroy() must be called before the destructor.
+  DCHECK(queries_[0] == 0);
+  DCHECK(queries_[1] == 0);
+}
+
+void GPUTimer::Destroy(bool have_context) {
+  if (have_context) {
+    glDeleteQueries(2, queries_);
+  }
+  memset(queries_, 0, sizeof(queries_));
 }
 
 void GPUTimer::Start() {