Add comment explianing memory policy on Mac.

content/common/gpu/gpu_memory_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 "content/common/gpu/gpu_memory_manager.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 747 matching lines @@
         3 * client_state->managed_memory_stats_.bytes_nice_to_have / 4;
 
     // Populate and send the allocation to the client
     GpuMemoryAllocation allocation;
 
     allocation.browser_allocation.suggest_have_frontbuffer =
         !client_state->hibernated_;
 
     allocation.renderer_allocation.bytes_limit_when_visible =
         client_state->bytes_allocation_when_visible_;
+    // Use a more conservative memory allocation policy on Mac because the
+    // platform is unstable when under memory pressure.
+    // http://crbug.com/141377
     allocation.renderer_allocation.priority_cutoff_when_visible =
 #if defined(OS_MACOSX)
         GpuMemoryAllocationForRenderer::kPriorityCutoffAllowNiceToHave;
 #else
         GpuMemoryAllocationForRenderer::kPriorityCutoffAllowEverything;
 #endif
 
     allocation.renderer_allocation.bytes_limit_when_not_visible =
         client_state->bytes_allocation_when_nonvisible_;
     allocation.renderer_allocation.priority_cutoff_when_not_visible =
@@ skipping 99 matching lines @@
 
 void GpuMemoryManager::RemoveClientFromList(
     GpuMemoryManagerClientState* client_state) {
   DCHECK(client_state->list_iterator_valid_);
   ClientStateList* client_list = GetClientList(client_state);
   client_list->erase(client_state->list_iterator_);
   client_state->list_iterator_valid_ = false;
 }
 
 }  // namespace content