Add UMA metrics for desktop memory pressure notifications.

chrome/browser/memory/tab_manager.cc

Index: chrome/browser/memory/tab_manager.cc
diff --git a/chrome/browser/memory/tab_manager.cc b/chrome/browser/memory/tab_manager.cc
index d26739073f7d3ddaab7f404f1358713d54f50fcf..6fbf52a66c21c073796cd3cfed4ce35c461d0dc9 100644
--- a/chrome/browser/memory/tab_manager.cc
+++ b/chrome/browser/memory/tab_manager.cc
@@ -919,6 +919,7 @@ TimeTicks TabManager::NowTicks() const {
 }
 
 void TabManager::DoChildProcessDispatch() {
+printf("TabManager::DoChildProcessDispatch\n");
   // If Chrome is shutting down, do not do anything.
   if (g_browser_process->IsShuttingDown())
     return;
@@ -929,6 +930,7 @@ void TabManager::DoChildProcessDispatch() {
   // 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;
@@ -954,6 +956,7 @@ void TabManager::DoChildProcessDispatch() {
 
       // Notify the renderer.
       notify_renderer_process_.Run(*rit, level);
+printf("   ...notified renderer %x\n", (int)(intptr_t)(*rit));
       notified = true;
       break;
     }