Constify SkFlattenable::getFactory().

This allows us to also constify the argument of
SkFlattenableWriteBuffer::writeFlattenable() - which I've recently found
myself const-casting for no apparent good reason.

R=bungeman@google.com, mtklein@google.com, reed@google.com

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/29143005

git-svn-id: http://skia.googlecode.com/svn/trunk@11862 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkDashPathEffect.cpp b/src/effects/SkDashPathEffect.cpp
index be06591..4aa46ab 100644
--- a/src/effects/SkDashPathEffect.cpp
+++ b/src/effects/SkDashPathEffect.cpp
@@ -528,7 +528,7 @@
     return true;
 }
 
-SkFlattenable::Factory SkDashPathEffect::getFactory() {
+SkFlattenable::Factory SkDashPathEffect::getFactory() const {
     return fInitialDashLength < 0 ? NULL : CreateProc;
 }