Add support for IMG's MSAA extension.
Review URL: https://codereview.chromium.org/12875005

git-svn-id: http://skia.googlecode.com/svn/trunk@8241 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/gl/GrGLDefines.h b/src/gpu/gl/GrGLDefines.h
index e0e8398..2ab9570 100644
--- a/src/gpu/gl/GrGLDefines.h
+++ b/src/gpu/gl/GrGLDefines.h
@@ -658,6 +658,8 @@
 #define GR_GL_DEPTH24_STENCIL8               0x88F0
 
 #define GR_GL_MAX_SAMPLES                    0x8D57
+// GL_IMG_multisampled_render_to_texture uses a different value for GL_MAX_SAMPLES
+#define GR_GL_MAX_SAMPLES_IMG                0x9135
 
 #define GR_GL_RENDERBUFFER_WIDTH             0x8D42
 #define GR_GL_RENDERBUFFER_HEIGHT            0x8D43