Add experimental feature for CompositingOptimizations

Bug: 1115577

Change-Id: Ia604e6feffcff7566a6bc4d433c946ac9f667bc6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2351401Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797506}

third_party/blink/common/features.cc

@@ -687,5 +687,8 @@ bool IsParkableStringsToDiskEnabled() {
 const base::Feature kCrOSAutoSelect{"CrOSAutoSelect",
                                     base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kCompositingOptimizations{
+    "CompositingOptimizations", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace blink

third_party/blink/public/common/features.h

@@ -276,6 +276,8 @@ BLINK_COMMON_EXPORT bool IsParkableStringsToDiskEnabled();
 
 BLINK_COMMON_EXPORT extern const base::Feature kCrOSAutoSelect;
 
+BLINK_COMMON_EXPORT extern const base::Feature kCompositingOptimizations;
+
 }  // namespace features
 }  // namespace blink