cc: Do a safe intersect when gathering images.

cc/playback/discardable_image_map.cc

Index: cc/playback/discardable_image_map.cc
diff --git a/cc/playback/discardable_image_map.cc b/cc/playback/discardable_image_map.cc
index 840de37a95686e3cd38a9d5066cf0b1646ff868a..822d49b6e4ca93097c12af58ed3548ad7e024007 100644
--- a/cc/playback/discardable_image_map.cc
+++ b/cc/playback/discardable_image_map.cc
@@ -24,6 +24,33 @@ SkRect MapRect(const SkMatrix& matrix, const SkRect& src) {
   return dst;
 }
 
+// Returns a rect clamped to |max_size|. Note that |paint_rect| should intersect
+// or be contained by a rect defined by (0, 0) and |max_size|.
+gfx::Rect SafeClampPaintRectToSize(const SkRect& paint_rect,
+                                   const gfx::Size& max_size) {
+  // bounds_rect.x() + bounds_rect.width() (aka bounds_rect.right()) might
+  // overflow integer bounds, so do custom intersect, since gfx::Rect::Intersect
+  // uses bounds_rect.right().
+  gfx::RectF bounds_rect = gfx::SkRectToRectF(paint_rect);
+  float x_offset_if_negative = bounds_rect.x() < 0.f ? bounds_rect.x() : 0.f;
+  float y_offset_if_negative = bounds_rect.y() < 0.f ? bounds_rect.y() : 0.f;
+  bounds_rect.set_x(std::max(0.f, bounds_rect.x()));
+  bounds_rect.set_y(std::max(0.f, bounds_rect.y()));
+
+  // Verify that the rects intersect or that bound_rect is contained by
+  // max_size.
+  DCHECK_GE(bounds_rect.width(), -x_offset_if_negative);
+  DCHECK_GE(bounds_rect.height(), -y_offset_if_negative);
+  DCHECK_GE(max_size.width(), bounds_rect.x());
+  DCHECK_GE(max_size.height(), bounds_rect.y());
+
+  bounds_rect.set_width(std::min(bounds_rect.width() + x_offset_if_negative,
+                                 max_size.width() - bounds_rect.x()));
+  bounds_rect.set_height(std::min(bounds_rect.height() + y_offset_if_negative,
+                                  max_size.height() - bounds_rect.y()));
+  return gfx::ToEnclosingRect(bounds_rect);
+}
+
 namespace {
 
 // We're using an NWay canvas with no added canvases, so in effect
@@ -36,7 +63,8 @@ class DiscardableImagesMetadataCanvas : public SkNWayCanvas {
       std::vector<std::pair<DrawImage, gfx::Rect>>* image_set)
       : SkNWayCanvas(width, height),
         image_set_(image_set),
-        canvas_bounds_(SkRect::MakeIWH(width, height)) {}
+        canvas_bounds_(SkRect::MakeIWH(width, height)),
+        canvas_size_(width, height) {}
 
  protected:
   // we need to "undo" the behavior of SkNWayCanvas, which will try to forward
@@ -146,11 +174,12 @@ class DiscardableImagesMetadataCanvas : public SkNWayCanvas {
     src_rect.roundOut(&src_irect);
     image_set_->push_back(std::make_pair(
         DrawImage(std::move(image), src_irect, filter_quality, matrix),
-        gfx::ToEnclosingRect(gfx::SkRectToRectF(paint_rect))));
+        SafeClampPaintRectToSize(paint_rect, canvas_size_)));
   }
 
   std::vector<std::pair<DrawImage, gfx::Rect>>* image_set_;
   const SkRect canvas_bounds_;
+  const gfx::Size canvas_size_;
   std::vector<SkPaint> saved_paints_;
 };