Fix tab discarding reload count metric.

chrome/browser/ui/tabs/tab_discard_state.cc

Index: chrome/browser/ui/tabs/tab_discard_state.cc
diff --git a/chrome/browser/ui/tabs/tab_discard_state.cc b/chrome/browser/ui/tabs/tab_discard_state.cc
index 7a7e8f05592e7e53ab1f097f6cbd95f17e81544c..22d24316eff0bbe8e664b50d3f0b4f683e8a5a06 100644
--- a/chrome/browser/ui/tabs/tab_discard_state.cc
+++ b/chrome/browser/ui/tabs/tab_discard_state.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/ui/tabs/tab_discard_state.h"
 
+#include "base/metrics/histogram.h"
 #include "content/public/browser/web_contents.h"
 
 using content::WebContents;
@@ -43,6 +44,13 @@ bool TabDiscardState::IsDiscarded(WebContents* web_contents) {
 // static
 void TabDiscardState::SetDiscardState(WebContents* web_contents, bool state) {
   TabDiscardState* discard_state = TabDiscardState::Get(web_contents);

[chrisha, 2015/09/25 17:11:52]

Does this object only get called from a single thread?

Maybe add a thread-checker to make sure? Otherwise there's still a race
condition.

[Georges Khalil, 2015/09/25 18:36:25]

Should all be on the UI thread.

Added thread checker just in case.

+
+  if (discard_state->is_discarded_ && !state) {
+    static int reload_count = 0;
+    UMA_HISTOGRAM_CUSTOM_COUNTS("Tabs.Discard.ReloadCount", ++reload_count, 1,
+                                1000, 50);
+  }
+
   discard_state->is_discarded_ = state;
 }