Add GrEffect::updateKnownColorComponents(). It is used to determine whether the output of an effect has a constant output value for r,g,b, or a.
Review URL: https://codereview.appspot.com/7064057

git-svn-id: http://skia.googlecode.com/svn/trunk@7144 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 8521bdb..7d77970 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -753,6 +753,8 @@
     SkBitmap bitmap;
     shader.getGradientTableBitmap(&bitmap);
 
+    fIsOpaque = shader.isOpaque();
+
     GrTextureStripAtlas::Desc desc;
     desc.fWidth  = bitmap.width();
     desc.fHeight = 32;