Re-adding red texture support (by rolling back r3800)

http://code.google.com/p/skia/source/detail?r=3622 - for original review
http://crbug.com/125596 ('M20 windows renderer stability maze') - for issue



git-svn-id: http://skia.googlecode.com/svn/trunk@3802 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/gl/GrGLDefines.h b/include/gpu/gl/GrGLDefines.h
index af8c2a8..0e03b55 100644
--- a/include/gpu/gl/GrGLDefines.h
+++ b/include/gpu/gl/GrGLDefines.h
@@ -300,6 +300,8 @@
 #define GR_GL_PALETTE8_RGBA8                 0x8B96
 #define GR_GL_ALPHA8                         0x803C
 
+#define GR_GL_R8                             0x8229
+
 /* PixelType */
 /*      GL_UNSIGNED_BYTE */
 #define GR_GL_UNSIGNED_SHORT_4_4_4_4         0x8033