cc: Add image decode control in the compositor.

cc/tiles/tile_manager.cc

Index: cc/tiles/tile_manager.cc
diff --git a/cc/tiles/tile_manager.cc b/cc/tiles/tile_manager.cc
index 56e6971a8b746abed8966fadd810f73c9b59a854..7086e800b45081d8aaa5e24f3d09f4947c69585b 100644
--- a/cc/tiles/tile_manager.cc
+++ b/cc/tiles/tile_manager.cc
@@ -24,6 +24,7 @@
 #include "cc/tiles/tile.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 
+#include "ui/gfx/transform.h"
 namespace cc {
 namespace {
 
@@ -279,7 +280,6 @@ void TileManager::CleanUpReleasedTiles() {
     DCHECK(tiles_.find(tile->id()) != tiles_.end());
     tiles_.erase(tile->id());
 
-    image_decode_controller_.SubtractLayerUsedCount(tile->layer_id());
     delete tile;
   }
   released_tiles_.swap(tiles_to_retain);
@@ -627,7 +627,7 @@ void TileManager::ScheduleTasks(
     DCHECK(tile->draw_info().requires_resource());
     DCHECK(!tile->draw_info().resource_);
 
-    if (!tile->raster_task_.get())
+    if (!tile->raster_task_)
       tile->raster_task_ = CreateRasterTask(prioritized_tile);
 
     TaskSetCollection task_sets;
@@ -643,6 +643,7 @@ void TileManager::ScheduleTasks(
   // We must reduce the amount of unused resoruces before calling
   // ScheduleTasks to prevent usage from rising above limits.
   resource_pool_->ReduceResourceUsage();
+  image_decode_controller_.ReduceCacheUsage();
 
   // Schedule running of |raster_queue_|. This replaces any previously
   // scheduled tasks and effectively cancels all tasks not present
@@ -660,6 +661,8 @@ void TileManager::ScheduleTasks(
 scoped_refptr<RasterTask> TileManager::CreateRasterTask(
     const PrioritizedTile& prioritized_tile) {
   Tile* tile = prioritized_tile.tile();
+
+  // Get the resource.
   uint64_t resource_content_id = 0;
   Resource* resource = nullptr;
   if (use_partial_raster_ && tile->invalidated_id()) {
@@ -680,12 +683,16 @@ scoped_refptr<RasterTask> TileManager::CreateRasterTask(
 
   // Create and queue all image decode tasks that this tile depends on.
   ImageDecodeTask::Vector decode_tasks;
-  std::vector<DrawImage> images;
+  std::vector<DrawImage>& images = scheduled_draw_images_[tile->id()];
+  images.clear();
   prioritized_tile.raster_source()->GetDiscardableImagesInRect(
       tile->enclosing_layer_rect(), tile->contents_scale(), &images);
   for (const auto& image : images) {
-    decode_tasks.push_back(image_decode_controller_.GetTaskForImage(
-        image, tile->layer_id(), prepare_tiles_count_));
+    scoped_refptr<ImageDecodeTask> task =
+        image_decode_controller_.GetTaskForImageAndRef(image,
+                                                       prepare_tiles_count_);
+    if (task)
+      decode_tasks.push_back(task);
   }
 
   return make_scoped_refptr(new RasterTaskImpl(
@@ -712,6 +719,15 @@ void TileManager::OnRasterTaskCompleted(
   orphan_raster_tasks_.push_back(tile->raster_task_);
   tile->raster_task_ = nullptr;
 
+  // Unref all the images.
+  auto images_it = scheduled_draw_images_.find(tile->id());
+  const std::vector<DrawImage>& images = images_it->second;
+  for (const auto& image : images) {
+    const DrawImage& scaled_image = image.ApplyScale(tile->contents_scale());
+    image_decode_controller_.UnrefImage(scaled_image);
+  }
+  scheduled_draw_images_.erase(images_it);
+
   if (was_canceled) {
     ++flush_stats_.canceled_count;
     // TODO(ericrk): If more partial raster work is done in the future, it may
@@ -766,7 +782,6 @@ ScopedTilePtr TileManager::CreateTile(const Tile::CreateInfo& info,
   DCHECK(tiles_.find(tile->id()) == tiles_.end());
 
   tiles_[tile->id()] = tile.get();
-  image_decode_controller_.AddLayerUsedCount(tile->layer_id());
   return tile;
 }