Update from https://crrev.com/320343

cc/resources/pixel_ref_map.cc

+// Copyright 2015 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/resources/pixel_ref_map.h"
+
+#include <algorithm>
+#include <limits>
+
+#include "cc/base/util.h"
+#include "cc/resources/picture.h"
+#include "skia/ext/pixel_ref_utils.h"
+
+namespace cc {
+
+PixelRefMap::PixelRefMap(const gfx::Size& cell_size) : cell_size_(cell_size) {
+  DCHECK(!cell_size.IsEmpty());
+}
+
+PixelRefMap::~PixelRefMap() {
+}
+
+void PixelRefMap::GatherPixelRefsFromPicture(SkPicture* picture) {
+  DCHECK(picture);
+
+  int min_x = std::numeric_limits<int>::max();
+  int min_y = std::numeric_limits<int>::max();
+  int max_x = 0;
+  int max_y = 0;
+
+  skia::DiscardablePixelRefList pixel_refs;
+  skia::PixelRefUtils::GatherDiscardablePixelRefs(picture, &pixel_refs);
+  for (skia::DiscardablePixelRefList::const_iterator it = pixel_refs.begin();
+       it != pixel_refs.end(); ++it) {
+    gfx::Point min(
+        RoundDown(static_cast<int>(it->pixel_ref_rect.x()), cell_size_.width()),
+        RoundDown(static_cast<int>(it->pixel_ref_rect.y()),
+                  cell_size_.height()));
+    gfx::Point max(
+        RoundDown(static_cast<int>(std::ceil(it->pixel_ref_rect.right())),
+                  cell_size_.width()),
+        RoundDown(static_cast<int>(std::ceil(it->pixel_ref_rect.bottom())),
+                  cell_size_.height()));
+
+    for (int y = min.y(); y <= max.y(); y += cell_size_.height()) {
+      for (int x = min.x(); x <= max.x(); x += cell_size_.width()) {
+        PixelRefMapKey key(x, y);
+        data_hash_map_[key].push_back(it->pixel_ref);
+      }
+    }
+
+    min_x = std::min(min_x, min.x());
+    min_y = std::min(min_y, min.y());
+    max_x = std::max(max_x, max.x());
+    max_y = std::max(max_y, max.y());
+  }
+
+  min_pixel_cell_ = gfx::Point(min_x, min_y);
+  max_pixel_cell_ = gfx::Point(max_x, max_y);
+}
+
+base::LazyInstance<PixelRefs> PixelRefMap::Iterator::empty_pixel_refs_;
+
+PixelRefMap::Iterator::Iterator()
+    : target_pixel_ref_map_(NULL),
+      current_pixel_refs_(empty_pixel_refs_.Pointer()),
+      current_index_(0),
+      min_point_(-1, -1),
+      max_point_(-1, -1),
+      current_x_(0),
+      current_y_(0) {
+}
+
+PixelRefMap::Iterator::Iterator(const gfx::Rect& rect, const Picture* picture)
+    : target_pixel_ref_map_(&(picture->pixel_refs_)),
+      current_pixel_refs_(empty_pixel_refs_.Pointer()),
+      current_index_(0) {
+  gfx::Rect layer_rect = picture->layer_rect_;
+  gfx::Size cell_size = target_pixel_ref_map_->cell_size_;
+  DCHECK(!cell_size.IsEmpty());
+  gfx::Rect query_rect(rect);
+  // Early out if the query rect doesn't intersect this picture.
+  if (!query_rect.Intersects(layer_rect)) {
+    min_point_ = gfx::Point(0, 0);
+    max_point_ = gfx::Point(0, 0);
+    current_x_ = 1;
+    current_y_ = 1;
+    return;
+  }
+
+  // First, subtract the layer origin as cells are stored in layer space.
+  query_rect.Offset(-layer_rect.OffsetFromOrigin());
+
+  // We have to find a cell_size aligned point that corresponds to
+  // query_rect. Point is a multiple of cell_size.
+  min_point_ = gfx::Point(RoundDown(query_rect.x(), cell_size.width()),
+                          RoundDown(query_rect.y(), cell_size.height()));
+  max_point_ =
+      gfx::Point(RoundDown(query_rect.right() - 1, cell_size.width()),
+                 RoundDown(query_rect.bottom() - 1, cell_size.height()));
+
+  // Limit the points to known pixel ref boundaries.
+  min_point_ = gfx::Point(
+      std::max(min_point_.x(), target_pixel_ref_map_->min_pixel_cell_.x()),
+      std::max(min_point_.y(), target_pixel_ref_map_->min_pixel_cell_.y()));
+  max_point_ = gfx::Point(
+      std::min(max_point_.x(), target_pixel_ref_map_->max_pixel_cell_.x()),
+      std::min(max_point_.y(), target_pixel_ref_map_->max_pixel_cell_.y()));
+
+  // Make the current x be cell_size.width() less than min point, so that
+  // the first increment will point at min_point_.
+  current_x_ = min_point_.x() - cell_size.width();
+  current_y_ = min_point_.y();
+  if (current_y_ <= max_point_.y())
+    ++(*this);
+}
+
+PixelRefMap::Iterator::~Iterator() {
+}
+
+PixelRefMap::Iterator& PixelRefMap::Iterator::operator++() {
+  ++current_index_;
+  // If we're not at the end of the list, then we have the next item.
+  if (current_index_ < current_pixel_refs_->size())
+    return *this;
+
+  DCHECK(current_y_ <= max_point_.y());
+  while (true) {
+    gfx::Size cell_size = target_pixel_ref_map_->cell_size_;
+
+    // Advance the current grid cell.
+    current_x_ += cell_size.width();
+    if (current_x_ > max_point_.x()) {
+      current_y_ += cell_size.height();
+      current_x_ = min_point_.x();
+      if (current_y_ > max_point_.y()) {
+        current_pixel_refs_ = empty_pixel_refs_.Pointer();
+        current_index_ = 0;
+        break;
+      }
+    }
+
+    // If there are no pixel refs at this grid cell, keep incrementing.
+    PixelRefMapKey key(current_x_, current_y_);
+    PixelRefHashmap::const_iterator iter =
+        target_pixel_ref_map_->data_hash_map_.find(key);
+    if (iter == target_pixel_ref_map_->data_hash_map_.end())
+      continue;
+
+    // We found a non-empty list: store it and get the first pixel ref.
+    current_pixel_refs_ = &iter->second;
+    current_index_ = 0;
+    break;
+  }
+  return *this;
+}
+
+}  // namespace cc