cc: Interface to evict images from cc image decode cache.

cc/tiles/gpu_image_decode_cache.cc

 // Copyright 2016 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/tiles/gpu_image_decode_cache.h"
 
 #include <inttypes.h>
 
 #include "base/auto_reset.h"
 #include "base/debug/alias.h"
@@ skipping 605 matching lines @@
     }
 
     it = persistent_cache_.Erase(it);
   }
 }
 
 size_t GpuImageDecodeCache::GetMaximumMemoryLimitBytes() const {
   return normal_max_cache_bytes_;
 }
 
+void GpuImageDecodeCache::NotifyImageUnused(uint32_t skimage_id) {
+  auto it = persistent_cache_.Peek(skimage_id);
+  if (it != persistent_cache_.end() && !it->second->decode.is_locked()) {

[vmpstr, 2017/06/19 16:34:41]

I _believe_ you can still mark things as orphaned (although you can't erase
them) if they are locked. +ericrk to confirm. So, I think this looks fine but I
think we can do slightly better by just reworking the if-conditions here.

[ericrk, 2017/06/19 17:09:30]

Agreed - you shouldn't need to check is_locked here:

In the case where we have any refs, and you set is_orphaned, we can be locked,
this won't cause problems.

In the case where we have no refs, we must never be locked (you can
DCHECK(!is_locked)).

[sohan, 2017/06/20 13:31:39]

Done.

+    if (it->second->decode.ref_count != 0 ||
+        it->second->upload.ref_count != 0) {
+      it->second->is_orphaned = true;
+    } else if (it->second->upload.image()) {
+      bytes_used_ -= it->second->size;
+      images_pending_deletion_.push_back(it->second->upload.image());
+      it->second->upload.SetImage(nullptr);
+      it->second->upload.budgeted = false;
+    }
+    persistent_cache_.Erase(it);
+  }
+}
+
 bool GpuImageDecodeCache::OnMemoryDump(
     const base::trace_event::MemoryDumpArgs& args,
     base::trace_event::ProcessMemoryDump* pmd) {
   using base::trace_event::MemoryAllocatorDump;
   using base::trace_event::MemoryAllocatorDumpGuid;
   using base::trace_event::MemoryDumpLevelOfDetail;
 
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "GpuImageDecodeCache::OnMemoryDump");
 
@@ skipping 710 matching lines @@
 
 void GpuImageDecodeCache::OnPurgeMemory() {
   base::AutoLock lock(lock_);
   // Temporary changes |memory_state_| to free up cache as much as possible.
   base::AutoReset<base::MemoryState> reset(&memory_state_,
                                            base::MemoryState::SUSPENDED);
   EnsureCapacity(0);
 }
 
 }  // namespace cc