Animations: Implement runtime flag for enabling compositor animation timelines.

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 18b8884dc44c0f37e247f7c4c528d23b40fb5565..238862f8d4f400e0bda178cc36b805b7df939f54 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -288,6 +288,10 @@ const char kDisableAcceleratedJpegDecoding[] =
 const char kEnableBleedingEdgeRenderingFastPaths[] =
     "enable-bleeding-edge-rendering-fast-paths";
 
+// Enables new cc/animation system (Project Heaviside). crbug.com/394772
+const char kEnableCompositorAnimationTimelines[] =
+    "enable-compositor-animation-timelines";
+
 // Enables LCD text.
 const char kEnableLCDText[]                 = "enable-lcd-text";