cros: Record UMA stats for tab discards in low memory conditions

* Per discussion with jar@, bin users into categories by number of tabs they have open as a proxy for how "heavily" they use Chrome.
* Separately track time-to-first-discard, as that should be longer as users take a little while to open up all their tabs.
* Also report snapshot of system-wide memory consumption at the time of the discard, to investigate tuning the kernel low-memory signal threshold.

BUG=123179
TEST=use chrome://discards to discard a few tabs, then check chrome://histograms and search for "TabDiscard" to verify the discards were counted

Review URL: https://chromiumcodereview.appspot.com/9969189

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@132811 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 4 deletions

diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index b7c90ee..66744f5 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -3539,8 +3539,9 @@ void Browser::ActiveTabChanged(TabContentsWrapper* old_contents,
         base::TERMINATION_STATUS_PROCESS_WAS_KILLED) {
     const CommandLine& parsed_command_line = *CommandLine::ForCurrentProcess();
     if (parsed_command_line.HasSwitch(switches::kReloadKilledTabs)) {
-      // Log to track down crash crbug.com/119068
       LOG(WARNING) << "Reloading killed tab at " << index;
+      static int reload_count = 0;
+      HISTOGRAM_COUNTS_10000("Tabs.SadTab.ReloadCount", ++reload_count);
       Reload(CURRENT_TAB);
       did_reload = true;
     }
@@ -3548,9 +3549,9 @@ void Browser::ActiveTabChanged(TabContentsWrapper* old_contents,
 
   // Discarded tabs always get reloaded.
   if (!did_reload && IsTabDiscarded(index)) {
-    // Log to track down crash crbug.com/119068
-    LOG(WARNING) << "Reloading discarded tab at " << index
-        << " gesture " << user_gesture;
+    LOG(WARNING) << "Reloading discarded tab at " << index;
+    static int reload_count = 0;
+    HISTOGRAM_COUNTS_10000("Tabs.Discard.ReloadCount", ++reload_count);
     Reload(CURRENT_TAB);
   }