cc: Don't activate rasterize on demand when we have 0 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 493 matching lines @@
       return;
     }
 
     FreeResourcesForReleasedTiles();
 
     resource_pool_->ReduceResourceUsage();
 
     // We don't reserve memory for required-for-activation tiles during
     // accelerated gestures, so we just postpone activation when we don't
     // have these tiles, and activate after the accelerated gesture.
+    // Likewise if we don't have any memory (as is the case when we're
+    // invisible), if we have tiles that aren't ready, then we shouldn't

[reveman, 2014/09/23 02:38:54]

Why is 0 the magic number here? Seems wrong to assume that memory limit is 0
when invisible. What if it's 1 byte or the size of 5 tiles?

Would it be better to not allow rasterize-on-demand unless visible?

[vmpstr, 2014/09/23 15:29:22]

Good point. Do you think we should make it a part of global_state_ or pass it to
ManageTiles as a separate variable? I don't really think adding another client
function is appropriate here since we can just directly pass the value.

[reveman, 2014/09/23 16:39:11]

Maybe it's fine to just use "global_state_.memory_limit_policy != ALLOW_NOTHING"
here if we just update the description in tile_priority.h to make it more
explicit that this policy is always used when invisible. Wdyt?

[vmpstr, 2014/09/23 17:25:32]

Done.

+    // activate as activation can cause checkerboards.
     bool allow_rasterize_on_demand =
-        global_state_.tree_priority != SMOOTHNESS_TAKES_PRIORITY;
+        global_state_.tree_priority != SMOOTHNESS_TAKES_PRIORITY &&
+        global_state_.hard_memory_limit_in_bytes != 0;
 
     // Use on-demand raster for any required-for-activation tiles that have not
     // been been assigned memory after reaching a steady memory state. This
     // ensures that we activate even when OOM.
     for (TileMap::iterator it = tiles_.begin(); it != tiles_.end(); ++it) {
       Tile* tile = it->second;
       ManagedTileState& mts = tile->managed_state();
       ManagedTileState::TileVersion& tile_version =
           mts.tile_versions[mts.raster_mode];
 
@@ skipping 653 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