Track UMA stats for running out of tile memory

cc/resources/tile_manager.cc

 // Copyright 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 "cc/resources/tile_manager.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 
@@ skipping 856 matching lines @@
   // OOM reporting uses hard-limit, soft-OOM is normal depending on limit.
   ever_exceeded_memory_budget_ |= oomed_hard;
   if (ever_exceeded_memory_budget_) {
     TRACE_COUNTER_ID2("cc",
                       "over_memory_budget",
                       this,
                       "budget",
                       global_state_.hard_memory_limit_in_bytes,
                       "over",
                       bytes_that_exceeded_memory_budget);
+
+    UMA_HISTOGRAM_BOOLEAN("TileManager.ExceededMemoryBudget", true);

[Ilya Sherman, 2014/07/02 21:08:37]

I strongly encourage you to build in a baseline for this metric.  Not all Chrome
users report UMA data, and not all UMA users use Chrome equally.  Suppose you
see that in a day, 10,000 users exceeded the memory budget.  What does that tell
you?  I bet that you'd deduce the answer by comparing 10,000 to a baseline that
is currently implicit.  Rather than having that baseline be implicit, which
requires every consumer of this metric to correctly identify and compute the
implicit baseline, you'd be better off building in an explicit baseline.

[sivag, 2014/07/03 14:24:08]

Thanks for the input.
Do we want to add the custom counts here, is that what you mean by baseline?

   }
   memory_stats_from_last_assign_.total_budget_in_bytes =
       global_state_.hard_memory_limit_in_bytes;
   memory_stats_from_last_assign_.bytes_allocated =
       hard_bytes_allocatable - hard_bytes_left;
   memory_stats_from_last_assign_.bytes_unreleasable =
       resource_pool_->acquired_memory_usage_bytes() - bytes_releasable_;
   memory_stats_from_last_assign_.bytes_over = bytes_that_exceeded_memory_budget;
 }
 
@@ skipping 689 matching lines @@
   TRACE_EVENT0("cc", "TileManager::CheckIfReadyToActivate");
 
   rasterizer_->CheckForCompletedTasks();
   did_check_for_completed_tasks_since_last_schedule_tasks_ = true;
 
   if (IsReadyToActivate())
     client_->NotifyReadyToActivate();
 }
 
 }  // namespace cc