cc: Stop using transfer buffer limit for 1-copy rasterizer.

It doesn't make sense for 1-copy rasterizer where we can
control the exact amount of memory used to be affected
by the transfer buffer limit.

This sets the upper bound to 32 resources, which is reduced
to 0 when invisible. A simple constant like this is likely
what we want long term.

BUG=406404

Review URL: https://codereview.chromium.org/597833002

Cr-Commit-Position: refs/heads/master@{#296423}

cc/trees/layer_tree_host_impl.cc

@@ -129,6 +129,11 @@ unsigned GetMapImageTextureTarget(cc::ContextProvider* context_provider) {
   return GL_TEXTURE_2D;
 }
 
+size_t GetMaxStagingResourceCount() {
+  // Upper bound for number of staging resource to allow.
+  return 32;
+}
+
 }  // namespace
 
 namespace cc {
@@ -264,8 +269,7 @@ LayerTreeHostImpl::LayerTreeHostImpl(
       micro_benchmark_controller_(this),
       need_to_update_visible_tiles_before_draw_(false),
       shared_bitmap_manager_(manager),
-      id_(id),
-      transfer_buffer_memory_limit_(0u) {
+      id_(id) {
   DCHECK(proxy_->IsImplThread());
   DidVisibilityChange(this, visible_);
   animation_registrar_->set_supports_scroll_animations(
@@ -1238,14 +1242,13 @@ void LayerTreeHostImpl::UpdateTileManagerMemoryPolicy(
       unused_memory_limit_in_bytes,
       global_tile_state_.num_resources_limit);
 
-  // Staging pool resources are used as transfer buffers so we use
-  // |transfer_buffer_memory_limit_| as the memory limit for this resource pool.
+  // Release all staging resources when invisible.
   if (staging_resource_pool_) {
     staging_resource_pool_->CheckBusyResources();
     staging_resource_pool_->SetResourceUsageLimits(
-        visible_ ? transfer_buffer_memory_limit_ : 0,
-        transfer_buffer_memory_limit_,
-        std::numeric_limits<size_t>::max());
+        std::numeric_limits<size_t>::max(),
+        std::numeric_limits<size_t>::max(),
+        visible_ ? GetMaxStagingResourceCount() : 0);
   }
 
   DidModifyTilePriorities();
@@ -1963,9 +1966,6 @@ void LayerTreeHostImpl::CreateAndSetTileManager() {
   DCHECK(proxy_->ImplThreadTaskRunner());
 
   ContextProvider* context_provider = output_surface_->context_provider();
-  transfer_buffer_memory_limit_ =
-      GetMaxTransferBufferUsageBytes(context_provider, settings_.refresh_rate);
-
   if (use_gpu_rasterization_ && context_provider) {
     resource_pool_ =
         ResourcePool::Create(resource_provider_.get(),
@@ -2004,7 +2004,8 @@ void LayerTreeHostImpl::CreateAndSetTileManager() {
         RasterWorkerPool::GetTaskGraphRunner(),
         context_provider,
         resource_provider_.get(),
-        transfer_buffer_memory_limit_);
+        GetMaxTransferBufferUsageBytes(context_provider,
+                                       settings_.refresh_rate));
   } else {
     resource_pool_ =
         ResourcePool::Create(resource_provider_.get(),

cc/trees/layer_tree_host_impl.h

@@ -698,8 +698,6 @@ class CC_EXPORT LayerTreeHostImpl
 
   std::set<SwapPromiseMonitor*> swap_promise_monitor_;
 
-  size_t transfer_buffer_memory_limit_;
-
   std::vector<PictureLayerImpl*> picture_layers_;
   std::vector<PictureLayerImpl::Pair> picture_layer_pairs_;