Add MSAA configs to bench.

include/gpu/GrContext.h

Index: include/gpu/GrContext.h
===================================================================
--- include/gpu/GrContext.h	(revision 8174)
+++ include/gpu/GrContext.h	(working copy)
@@ -251,12 +251,6 @@
      */
     int getMaxTextureSize() const;
 
-    /**
-     * Return the max width or height of a render target supported by the
-     * current GPU.
-     */
-    int getMaxRenderTargetSize() const;
-
     ///////////////////////////////////////////////////////////////////////////
     // Render targets
 
@@ -280,6 +274,18 @@
      */
     bool isConfigRenderable(GrPixelConfig config) const;
 
+    /**
+     * Return the max width or height of a render target supported by the
+     * current GPU.
+     */
+    int getMaxRenderTargetSize() const;
+
+    /**
+     * Returns the max sample count for a render target. It will be 0 if MSAA
+     * is not supported.
+     */
+    int getMaxSampleCount() const;
+
     ///////////////////////////////////////////////////////////////////////////
     // Backend Surfaces