alpha threshold bitmap shader

Committed: http://code.google.com/p/skia/source/detail?r=11122

R=reed@google.com

Author: bsalomon@google.com

Review URL: https://chromiumcodereview.appspot.com/23707019

git-svn-id: http://skia.googlecode.com/svn/trunk@11131 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/GrEffect.h b/include/gpu/GrEffect.h
index 942e580..a84810c 100644
--- a/include/gpu/GrEffect.h
+++ b/include/gpu/GrEffect.h
@@ -204,8 +204,9 @@
 protected:
     /**
      * Subclasses call this from their constructor to register GrTextureAccesses. The effect
-     * subclass manages the lifetime of the accesses (this function only stores a pointer). This
-     * must only be called from the constructor because GrEffects are immutable.
+     * subclass manages the lifetime of the accesses (this function only stores a pointer). The
+     * GrTextureAccess is typically a member field of the GrEffet subclass. This must only be
+     * called from the constructor because GrEffects are immutable.
      */
     void addTextureAccess(const GrTextureAccess* textureAccess);