Add feature for main frame before activation.

content/public/common/content_features.cc

Index: content/public/common/content_features.cc
diff --git a/content/public/common/content_features.cc b/content/public/common/content_features.cc
index 74151991f3c0399487be20d7b0d664c14f9473e0..c9a43466c8e2712c934c757faee1b5aca23d2a27 100644
--- a/content/public/common/content_features.cc
+++ b/content/public/common/content_features.cc
@@ -30,10 +30,11 @@ const base::Feature kDownloadResumption{"DownloadResumption",
 const base::Feature kDocumentWriteEvaluator{"DocumentWriteEvaluator",
                                             base::FEATURE_DISABLED_BY_DEFAULT};
 
-// Enable the material design playback UI for media elements.  This is always
-// on for OS_ANDROID, but may be enabled by experiment for other platforms.
-const base::Feature kNewMediaPlaybackUi{"NewMediaPlaybackUi",
-                                        base::FEATURE_ENABLED_BY_DEFAULT};
+// Can main thread be pipelined with activation. Always disabled for devices
+// with fewer than 4 cores irrespective of this flag. Can also be overridden by
+// --enable(disable)-main-frame-before-activation command line flag.
+const base::Feature kMainFrameBeforeActivation{
+    "MainFrameBeforeActivation", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // FeatureList definition for trials to enable the download button on
 // MediaDocument.
@@ -42,6 +43,11 @@ const base::Feature kMediaDocumentDownloadButton{
     base::FEATURE_DISABLED_BY_DEFAULT
 };
 
+// Enable the material design playback UI for media elements.  This is always
+// on for OS_ANDROID, but may be enabled by experiment for other platforms.
+const base::Feature kNewMediaPlaybackUi{"NewMediaPlaybackUi",
+                                        base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Non-validating reload on reload-to-refresh-content (e.g. pull-to-refresh).
 // See https://crbug.com/558829
 const base::Feature kNonValidatingReloadOnRefreshContent{