Add a command-line flag to set GPU rasterization multisampling.

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 8aecbca5333706d4bb98b0ccbf40fe12733d4120..0a42d6549f51925f1b6c4a9a4675e3fa7969ff8e 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -497,6 +497,11 @@ const char kForceFieldTrials[]              = "force-fieldtrials";
 // kEnableGpuRasterization flag.
 const char kForceGpuRasterization[]        = "force-gpu-rasterization";
 
+// The number of multisample antialiasing samples for GPU rasterization.
+// Requires MSAA support on GPU to have an effect. 0 disables MSAA.
+const char kGpuRasterizationMSAASampleCount[] =
+    "gpu-rasterization-msaa-sample-count";
+
 // Force renderer accessibility to be on instead of enabling it on demand when
 // a screen reader is detected. The disable-renderer-accessibility switch
 // overrides this if present.