Add a flag to allow renderer to use software compositor when GL compositor doesn't work.

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 88ee98c17173847579862c3494423485d3e5c81e..06f4645b9ba419def78c17e33bd9e6c576241304 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -515,9 +515,11 @@ const char kForceFieldTrials[]              = "force-fieldtrials";
 // overrides this if present.
 const char kForceRendererAccessibility[]    = "force-renderer-accessibility";
 
-// Force the compositor to use its software implementation instead of GL.
-const char kEnableSoftwareCompositingGLAdapter[] =
-    "enable-software-compositing-gl-adapter";
+// Allow the compositor to use its software implementation if GL fails.
+const char kEnableSoftwareCompositing[] = "enable-software-compositing";
+
+// Prevent the compositor from using its GPU implementation.
+const char kDisableGpuCompositing[] = "disable-gpu-compositing";
 
 // Passes gpu device_id from browser process to GPU process.
 const char kGpuDeviceID[]                   = "gpu-device-id";