Enforce 16byte alignment in shader contexts (patchset #1 id:1 of https://codereview.chromium.org/1759653004/ )"

This reverts commit e38bcaf24b00066e167e03a5ac63cf828914d747.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1763973002

TBR=

Review URL: https://codereview.chromium.org/1763973002
diff --git a/src/image/SkImageShader.cpp b/src/image/SkImageShader.cpp
index a07603c..4c7ded9 100644
--- a/src/image/SkImageShader.cpp
+++ b/src/image/SkImageShader.cpp
@@ -42,7 +42,7 @@
     return fImage->isOpaque();
 }
 
-size_t SkImageShader::contextSize(const ContextRec& rec) const {
+size_t SkImageShader::onContextSize(const ContextRec& rec) const {
     return SkBitmapProcShader::ContextSize(rec);
 }