Add feature for disabling directly composited images

We're planning on running an experiment to turn off this codepath. It's
unclear how to implement for CAP and could result in GPU memory
savings. Spot checked Google Maps mobile site, and it no longer
triggers this particular behavior.

Bug: 875110
Change-Id: Ie2bb7e03585a87ac07843e08177992a0f3b9c81b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1852192Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Daniel Libby <dlibby@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#705779}

third_party/blink/common/features.cc

@@ -402,5 +402,9 @@ const base::Feature kLowerJavaScriptPriorityWhenForceDeferred{
 const base::Feature kHtmlImportsRequestInitiatorLock{
     "HtmlImportsRequestInitiatorLock", base::FEATURE_ENABLED_BY_DEFAULT};
 
+// When 'enabled', directly compositing images is turned off.
+const base::Feature kDisableDirectlyCompositedImages{
+    "DisableDirectlyCompositedImages", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace blink

third_party/blink/public/common/features.h

@@ -128,6 +128,8 @@ BLINK_COMMON_EXPORT extern const base::Feature
 
 BLINK_COMMON_EXPORT extern const base::Feature kARIAAnnotationRoles;
 
+BLINK_COMMON_EXPORT extern const base::Feature kDisableDirectlyCompositedImages;
+
 }  // namespace features
 }  // namespace blink
 

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.cc

@@ -28,6 +28,7 @@
 #include <memory>
 
 #include "cc/layers/picture_layer.h"
+#include "third_party/blink/public/common/features.h"
 #include "third_party/blink/renderer/core/accessibility/apply_dark_mode.h"
 #include "third_party/blink/renderer/core/display_lock/display_lock_utilities.h"
 #include "third_party/blink/renderer/core/dom/dom_node_ids.h"
@@ -1753,6 +1754,10 @@ bool CompositedLayerMapping::ContainsPaintedContent() const {
 // compositing saves a backing store.
 bool CompositedLayerMapping::IsDirectlyCompositedImage() const {
   DCHECK(GetLayoutObject().IsImage());
+
+  if (base::FeatureList::IsEnabled(features::kDisableDirectlyCompositedImages))
+    return false;
+
   LayoutImage& image_layout_object = ToLayoutImage(GetLayoutObject());
 
   if (owning_layer_.HasBoxDecorationsOrBackground() ||