Enable partial recording if slimmingPaintDisplayItemCache is enabled

BUG=444163
R=enne@chromium.org
TBR=kbr@chromium.org (trivial change in render_widget_compositor.cc which is really related to cc/)

Review URL: https://codereview.chromium.org/913163004

Cr-Commit-Position: refs/heads/master@{#316244}

cc/resources/display_list_recording_source.cc

@@ -60,10 +60,9 @@ bool DisplayListRecordingSource::UpdateAndExpandInvalidation(
   }
 
   gfx::Rect old_recorded_viewport = recorded_viewport_;
-  // TODO(wangxianzhu): Blink slimming paint doesn't support incremental
-  // painting for now so we must record for the whole layer. Should measure
-  // performance and determine the best choice. Consider display item caching.
-  recorded_viewport_ = gfx::Rect(GetSize());
+  recorded_viewport_ = visible_layer_rect;
+  recorded_viewport_.Inset(-pixel_record_distance_, -pixel_record_distance_);
+  recorded_viewport_.Intersect(gfx::Rect(GetSize()));
 
   if (recorded_viewport_ != old_recorded_viewport) {
     // Invalidate newly-exposed and no-longer-exposed areas.

content/renderer/gpu/render_widget_compositor.cc

@@ -39,6 +39,7 @@
 #include "third_party/WebKit/public/platform/WebSelectionBound.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
 #include "third_party/WebKit/public/web/WebKit.h"
+#include "third_party/WebKit/public/web/WebRuntimeFeatures.h"
 #include "third_party/WebKit/public/web/WebWidget.h"
 #include "ui/gfx/frame_time.h"
 #include "ui/gfx/hud_font.h"
@@ -195,7 +196,12 @@ void RenderWidgetCompositor::Initialize() {
       !compositor_deps_->IsElasticOverscrollEnabled();
   settings.accelerated_animation_enabled =
       !cmd->HasSwitch(cc::switches::kDisableThreadedAnimation);
-  settings.use_display_lists = cmd->HasSwitch(switches::kEnableSlimmingPaint);
+  if (cmd->HasSwitch(switches::kEnableSlimmingPaint)) {
+    settings.use_display_lists = true;
+    blink::WebRuntimeFeatures::enableSlimmingPaint(true);
+    settings.record_full_layer =
+        !blink::WebRuntimeFeatures::slimmingPaintDisplayItemCacheEnabled();
+  }
 
   settings.default_tile_size = CalculateDefaultTileSize();
   if (cmd->HasSwitch(switches::kDefaultTileWidth)) {