Report user actions when gesture starts and stops in user_model.

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index f5326629a5ea23e3d1774672b43115ad96ed7761..9fcc4f2956903336d6d08e9a1bc5e909a5024630 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -16,6 +16,7 @@
 #include "base/macros.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/ref_counted.h"
+#include "base/metrics/user_metrics.h"
 #include "base/metrics/user_metrics_action.h"
 #include "base/observer_list.h"
 #include "base/strings/string16.h"
@@ -710,6 +711,9 @@ class CONTENT_EXPORT RenderThreadImpl
 
   StoragePartitionServicePtr storage_partition_service_;
 
+  // Callback for logging UMA user action.
+  base::ActionCallback action_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderThreadImpl);
 };