Remove DisableDirectlyCompositedImages flag

Experimental data unfortunately showed that it is not straightfoward to
simply remove the directly composited image feature (see:
https://crbug.com/875110#c22). This patch removes the plumbing added for
the flag.

Bug: 875110
Change-Id: Ib09f3ba13d3ab8759f9188ffb60cb80360ac24de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1982140
Auto-Submit: Philip Rogers <pdr@chromium.org>
Reviewed-by: Daniel Libby <dlibby@microsoft.com>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727595}

third_party/blink/common/features.cc

@@ -396,10 +396,6 @@ 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};
-
 // Enables redirecting subresources in the page to better compressed and
 // optimized versions to provide data savings.
 const base::Feature kSubresourceRedirect{"SubresourceRedirect",

third_party/blink/public/common/features.h

@@ -127,7 +127,6 @@ BLINK_COMMON_EXPORT extern const base::Feature
 
 BLINK_COMMON_EXPORT extern const base::Feature kARIAAnnotations;
 
-BLINK_COMMON_EXPORT extern const base::Feature kDisableDirectlyCompositedImages;
 BLINK_COMMON_EXPORT extern const base::Feature kCompositeCrossOriginIframes;
 BLINK_COMMON_EXPORT extern const base::Feature kVizHitTestOcclusionCheck;
 

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

@@ -28,7 +28,6 @@
 #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"
@@ -1576,9 +1575,6 @@ bool CompositedLayerMapping::ContainsPaintedContent() const {
 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() ||