Reduce max number of textures to 4 to make room for a larger class id in effect key

git-svn-id: http://skia.googlecode.com/svn/trunk@11538 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/GrBackendEffectFactory.h b/include/gpu/GrBackendEffectFactory.h
index 77cf2cc..6f5cb3b 100644
--- a/include/gpu/GrBackendEffectFactory.h
+++ b/include/gpu/GrBackendEffectFactory.h
@@ -40,7 +40,7 @@
          * GrGLEffects' control. So there is a dedicated part of the key which is combined
          * automatically with the bits produced by GrGLEffect::GenKey().
          */
-        kTextureKeyBits = 6,
+        kTextureKeyBits = 4,
         kAttribKeyBits = 6
     };