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

cc/tiles/gpu_image_decode_cache.cc

Index: cc/tiles/gpu_image_decode_cache.cc
diff --git a/cc/tiles/gpu_image_decode_cache.cc b/cc/tiles/gpu_image_decode_cache.cc
index 1dd9f10cd7a59d4859d6c062093a915cbbb48d55..21518b77998965d21a9a1ea1ad24351051d1eea9 100644
--- a/cc/tiles/gpu_image_decode_cache.cc
+++ b/cc/tiles/gpu_image_decode_cache.cc
@@ -623,6 +623,22 @@ 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) {