[blimp] Add SkPicture caching support.

blimp/common/compositor/reference_tracker.cc

Index: blimp/common/compositor/reference_tracker.cc
diff --git a/blimp/common/compositor/reference_tracker.cc b/blimp/common/compositor/reference_tracker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..aa3d43f8d1c3f1f5ec4c63ae6053b274a065f467
--- /dev/null
+++ b/blimp/common/compositor/reference_tracker.cc
@@ -0,0 +1,54 @@
+// 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 "blimp/common/compositor/reference_tracker.h"
+
+#include <stdint.h>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "base/logging.h"
+
+namespace blimp {
+
+ReferenceTracker::ReferenceTracker() {}
+
+ReferenceTracker::~ReferenceTracker() {}
+
+void ReferenceTracker::IncrementRefCount(uint32_t item) {
+  ++active_ref_counts_[item];
+}
+
+void ReferenceTracker::DecrementRefCount(uint32_t item) {
+  DCHECK_GT(active_ref_counts_[item], 0u);
+  --active_ref_counts_[item];
+}
+
+void ReferenceTracker::CommitRefCounts(std::vector<uint32_t>* added_entries,
+                                       std::vector<uint32_t>* removed_entries) {
+  DCHECK(added_entries);
+  DCHECK(removed_entries);
+  for (auto it = active_ref_counts_.begin(); it != active_ref_counts_.end();) {
+    uint32_t key = it->first;
+    uint32_t ref_count = it->second;
+    bool is_committed = committed_.count(key) > 0u;
+    if (ref_count > 0u) {
+      if (!is_committed) {
+        committed_.insert(key);

[Kevin M, 2016/06/21 21:35:04]

Add a one-line comment, like on 48?

[nyquist, 2016/06/24 11:11:15]

Done.

+        added_entries->push_back(key);
+      }
+      ++it;
+    } else {
+      if (is_committed) {
+        committed_.erase(key);
+        removed_entries->push_back(key);
+      }
+      // The entry has no references, so should not be staged anymore.
+      it = active_ref_counts_.erase(it);
+    }
+  }
+}
+
+}  // namespace blimp