Add UMA metrics for desktop memory pressure notifications.

chrome/browser/memory/tab_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/memory/tab_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <set>
@@ skipping 901 matching lines @@
 }
 
 TimeTicks TabManager::NowTicks() const {
   if (!test_tick_clock_)
     return TimeTicks::Now();
 
   return test_tick_clock_->NowTicks();
 }
 
 void TabManager::DoChildProcessDispatch() {
+printf("TabManager::DoChildProcessDispatch\n");
   // If Chrome is shutting down, do not do anything.
   if (g_browser_process->IsShuttingDown())
     return;
 
   if (!under_memory_pressure_)
     under_memory_pressure_ = true;
 
   // If the memory pressure condition has ended then stop dispatching messages.
   auto level = get_current_pressure_level_.Run();
   if (level == base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE) {
+printf("   ...no pressure\n");
     under_memory_pressure_ = false;
     notified_renderers_.clear();
     return;
   }
 
   // Get a vector of active renderers, from highest to lowest priority.
   auto renderers = GetOrderedRenderers();
 
   // The following code requires at least one renderer to be present or it will
   // busyloop. It's possible for no renderers to exist (we eliminate visible
   // renderers to avoid janking them), so bail early if that's the case.
   if (renderers.empty())
     return;
 
   // Notify a single renderer of memory pressure.
   bool notified = false;
   while (!notified) {
     // Notify the lowest priority renderer that hasn't been notified yet.
     for (auto rit = renderers.rbegin(); rit != renderers.rend(); ++rit) {
       // If this renderer has already been notified then look at the next one.
       if (!notified_renderers_.insert(*rit).second)
         continue;
 
       // Notify the renderer.
       notify_renderer_process_.Run(*rit, level);
+printf("   ...notified renderer %x\n", (int)(intptr_t)(*rit));
       notified = true;
       break;
     }
 
     // If all renderers were processed and none were notified, then all
     // renderers have already been notified. Clear the list and start again.
     if (!notified)
       notified_renderers_.clear();
 
     // This loop can only run at most twice. If it doesn't exit the first time
@@ skipping 44 matching lines @@
   // platform.
   std::string allow_multiple_discards = variations::GetVariationParamValue(
       features::kAutomaticTabDiscarding.name, "AllowMultipleDiscards");
   return (allow_multiple_discards != "true");
 #else
   return false;
 #endif
 }
 
 }  // namespace memory