[vr] Add a frame rate counter for the vr UI

cc/trees/frame_rate_counter.h

Index: cc/trees/frame_rate_counter.h
diff --git a/cc/trees/frame_rate_counter.h b/cc/trees/frame_rate_counter.h
index 83e8cf7151ffeaf97279dd75d8ed8f0a1e16e4fc..50e50a028656dd1c34b19b7cec53b5be2db3c102 100644
--- a/cc/trees/frame_rate_counter.h
+++ b/cc/trees/frame_rate_counter.h
@@ -12,12 +12,13 @@
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "cc/base/ring_buffer.h"
+#include "cc/cc_export.h"
 
 namespace cc {
 
 // This class maintains a history of timestamps, and provides functionality to
 // intelligently compute average frames per second.
-class FrameRateCounter {
+class CC_EXPORT FrameRateCounter {
  public:
   static std::unique_ptr<FrameRateCounter> Create(bool has_impl_thread);