[blimp] Add SkPicture caching support.

blimp/engine/renderer/blimp_engine_picture_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 "blimp/engine/renderer/blimp_engine_picture_cache.h"
+
+#include <map>
+#include <memory>
+#include <sstream>
+#include <vector>
+
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "blimp/common/compositor/blimp_picture_cache_registry.h"
+#include "cc/proto/picture_cache.h"
+#include "third_party/skia/include/core/SkPicture.h"
+#include "third_party/skia/include/core/SkStream.h"
+
+namespace blimp {
+namespace engine {
+
+BlimpEnginePictureCache::BlimpEnginePictureCache(
+    SkPixelSerializer* pixel_serializer)
+    : pixel_serializer_(pixel_serializer) {}
+
+BlimpEnginePictureCache::~BlimpEnginePictureCache() {}

[vmpstr, 2016/06/01 00:10:56]

= default

[nyquist, 2016/06/04 00:24:57]

Done.

+
+void BlimpEnginePictureCache::MarkPictureForUnregistration(
+    const SkPicture* picture) {
+  registry_.DecrementRefCount(picture->uniqueID());
+}
+
+void BlimpEnginePictureCache::MarkPictureForRegistration(
+    const SkPicture* picture) {
+  registry_.IncrementRefCount(picture->uniqueID());
+
+  // Do not serialize multiple times, even though the item is referred to from
+  // multiple places.
+  if (pictures_.find(picture->uniqueID()) != pictures_.end()) {

[vmpstr, 2016/06/01 00:10:56]

nit: braces optional 

[nyquist, 2016/06/04 00:24:57]

Yes, but we use them in //blimp, which is why my CL might seem very inconsistent
to you :-/

+    return;
+  }
+
+  // Use skia's serialize() method for now.
+  SkDynamicMemoryWStream stream;
+  picture->serialize(&stream, pixel_serializer_);
+  if (stream.bytesWritten() <= 0) {

[vmpstr, 2016/06/01 00:10:56]

Can you add a comment on when this can fail?

[nyquist, 2016/06/04 00:24:57]

From reading the serialization code, it seems that we'll always at least write a
byte, so I don't think it can. Changed to DCHECK.

+    DVLOG(1) << "Unable to serialize SkPicture with unique ID "
+             << picture->uniqueID();
+    return;
+  }
+
+  // Store the picture data until it is sent to the client.
+  cc::PictureData picture_data;
+  picture_data.unique_id = picture->uniqueID();
+  sk_sp<SkData> data(stream.copyToData());
+  picture_data.data = data;

[vmpstr, 2016/06/01 00:10:56]

the last two lines could be one line?

picture_data.data = stream.copyToData()?

or .reset if sk_sp has that. 

[nyquist, 2016/06/04 00:24:57]

Done.

+  pictures_[picture_data.unique_id] = picture_data;
+}
+
+cc::PictureCacheUpdate BlimpEnginePictureCache::CalculateCacheUpdateAndFlush() {
+  std::vector<uint32_t> added;
+  std::vector<uint32_t> removed;
+  registry_.Commit(&added, &removed);
+
+  // Create cache update consisting of new pictures.
+  cc::PictureCacheUpdate update;
+  for (const auto it : added) {
+    auto entry = pictures_.find(it);
+    if (entry == pictures_.end()) {
+      NOTREACHED() << "PictureMap does not contain entry " << it;
+      continue;
+    }
+    update.push_back(entry->second);
+  }
+
+  // All new items will be sent to client, so clear everything.
+  pictures_.clear();
+
+  return update;
+}
+
+}  // namespace engine
+}  // namespace blimp