Add support for IMG's MSAA extension.

src/gpu/gl/GrGLDefines.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 
 #ifndef GrGLDefines_DEFINED
@@ skipping 640 matching lines @@
 #define GR_GL_SRGB8_ALPHA8                   0x8C43
 #define GR_GL_DEPTH_COMPONENT16              0x81A5
 #define GR_GL_STENCIL_INDEX                  0x1901
 #define GR_GL_STENCIL_INDEX4                 0x8D47
 #define GR_GL_STENCIL_INDEX8                 0x8D48
 #define GR_GL_STENCIL_INDEX16                0x8D49
 #define GR_GL_DEPTH_STENCIL                  0x84F9
 #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
 #define GR_GL_RENDERBUFFER_INTERNAL_FORMAT   0x8D44
 #define GR_GL_RENDERBUFFER_RED_SIZE          0x8D50
 #define GR_GL_RENDERBUFFER_GREEN_SIZE        0x8D51
 #define GR_GL_RENDERBUFFER_BLUE_SIZE         0x8D52
 #define GR_GL_RENDERBUFFER_ALPHA_SIZE        0x8D53
 #define GR_GL_RENDERBUFFER_DEPTH_SIZE        0x8D54
 #define GR_GL_RENDERBUFFER_STENCIL_SIZE      0x8D55
@@ skipping 200 matching lines @@
 #define GR_GL_ADJACENT_PAIRS                                0x90AE
 #define GR_GL_FIRST_TO_REST                                 0x90AF
 
 //path gen modes
 #define GR_GL_PATH_GEN_MODE                                 0x90B0
 #define GR_GL_PATH_GEN_COEFF                                0x90B1
 #define GR_GL_PATH_GEN_COLOR_FORMAT                         0x90B2
 #define GR_GL_PATH_GEN_COMPONENTS                           0x90B3
 
 #endif