Disable force-compositing-mode experiment when using swiftshader.

chrome/browser/gpu_util.cc

Index: chrome/browser/gpu_util.cc
diff --git a/chrome/browser/gpu_util.cc b/chrome/browser/gpu_util.cc
index 10293ad9271f4987b4801617c2a774f415cdcd43..c2541180cd4fde9da5e53a7dc46eb9cc79da4294 100644
--- a/chrome/browser/gpu_util.cc
+++ b/chrome/browser/gpu_util.cc
@@ -193,6 +193,11 @@ void InitializeForceCompositingModeFieldTrial() {
     return;
 #endif
 
+  // The performance of accelerated compositing is too low with software
+  // rendering.
+  if (content::GpuDataManager::GetInstance()->ShouldUseSoftwareRendering())
+    return;
+
   // Don't activate the field trial if force-compositing-mode has been
   // explicitly disabled from the command line.
   if (CommandLine::ForCurrentProcess()->HasSwitch(