Use MSAA in GPU rasterization if Skia suggests it

cc/base/switches.cc

Index: cc/base/switches.cc
diff --git a/cc/base/switches.cc b/cc/base/switches.cc
index 1fb7ac98e37d6b3b87e1431a530bd25cd16a291e..a73a774d4e80697fda8b4375fb6366e166aabc9b 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -4,6 +4,8 @@
 
 #include "cc/base/switches.h"
 
+#include <string>
+
 #include "base/command_line.h"
 
 namespace cc {
@@ -37,8 +39,9 @@ const char kEnableTopControlsPositionCalculation[] =
     "enable-top-controls-position-calculation";
 
 // Allow heuristics to determine when a layer tile should be drawn with
-// the Skia GPU backend.  Only valid with GPU accelerated compositing +
-// impl-side painting.
+// a Skia GPU backend. The backend can be selected explicitly by
+// appending "={gpu,msaa4,msaa16}".
+// Only valid with GPU accelerated compositing + impl-side painting.
 const char kEnableGPURasterization[] = "enable-gpu-rasterization";
 
 // Disable GPU rasterization, i.e. rasterize on the CPU only.
@@ -176,6 +179,19 @@ bool IsGpuRasterizationEnabled() {
   return false;
 }
 
+GpuRasterizationType GetGpuRasterizationType() {
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+
+  std::string type =
+      command_line.GetSwitchValueASCII(switches::kEnableGPURasterization);
+  if (type == "msaa4")
+    return GpuRasterizationMsaa4;
+  else if (type == "msaa16")
+    return GpuRasterizationMsaa4;
+
+  return GpuRasterizationGpu;
+}
+
 bool IsImplSidePaintingEnabled() {
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();