Fix GPU tracing offset calculation on android.

gpu/command_buffer/service/gpu_timing.cc

Index: gpu/command_buffer/service/gpu_timing.cc
diff --git a/gpu/command_buffer/service/gpu_timing.cc b/gpu/command_buffer/service/gpu_timing.cc
index 8716448a4ad507c714a1b7c8a061271763d18906..302c3c493e847c0bfc1216f8bbac67dc9ec06645 100644
--- a/gpu/command_buffer/service/gpu_timing.cc
+++ b/gpu/command_buffer/service/gpu_timing.cc
@@ -23,11 +23,11 @@ GPUTimer::~GPUTimer() {
 void GPUTimer::Start() {
   // GL_TIMESTAMP and GL_TIMESTAMP_EXT both have the same value.
   glQueryCounter(queries_[0], GL_TIMESTAMP);
-  offset_ = gpu_timing_->CalculateTimerOffset();
 }
 
 void GPUTimer::End() {
   end_requested_ = true;
+  offset_ = gpu_timing_->CalculateTimerOffset();
   glQueryCounter(queries_[1], GL_TIMESTAMP);
 }