Add feature for main frame before activation.

content/public/common/content_features.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "build/build_config.h"
 #include "content/public/common/content_features.h"
 
 namespace features {
 
 // All features in alphabetical order.
@@ skipping 12 matching lines @@
 // permanently. See https://crbug.com/7648
 const base::Feature kDownloadResumption{"DownloadResumption",
                                         base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Speculatively pre-evaluate Javascript which will likely use document.write to
 // load an external script. The feature extracts the written markup and sends it
 // to the preload scanner.
 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.
 const base::Feature kMediaDocumentDownloadButton{
     "MediaDocumentDownloadButton",
     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{
     "NonValidatingReloadOnRefreshContent",
     base::FEATURE_DISABLED_BY_DEFAULT};
 
 // An experiment to optimize resource loading IPC for small resources.
 // http://crbug.com/580928
 const base::Feature kOptimizeIPCForSmallResource{
     "OptimizeForSmallResource",
@@ skipping 40 matching lines @@
 // we will not use replica editor and do a round trip to renderer to synchronize
 // with Blink data.
 const base::Feature kImeThread{"ImeThread", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // FeatureList definition for the Seccomp field trial.
 const base::Feature kSeccompSandboxAndroid{"SeccompSandboxAndroid",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 #endif
 
 }  // namespace features