Initial error handling code

I made it as simple as possible. The impact seems minimal and it should do what's necessary to make this code secure.

BUG=

Committed: http://code.google.com/p/skia/source/detail?r=11247

R=reed@google.com, scroggo@google.com, djsollen@google.com, sugoi@google.com, bsalomon@google.com, mtklein@google.com, senorblanco@google.com, senorblanco@chromium.org

Author: sugoi@chromium.org

Review URL: https://codereview.chromium.org/23021015

git-svn-id: http://skia.googlecode.com/svn/trunk@11922 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkTestImageFilters.cpp b/src/effects/SkTestImageFilters.cpp
index 788c33a..d0e21a3 100755
--- a/src/effects/SkTestImageFilters.cpp
+++ b/src/effects/SkTestImageFilters.cpp
@@ -78,4 +78,5 @@
 
 SkDownSampleImageFilter::SkDownSampleImageFilter(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {
     fScale = buffer.readScalar();
+    buffer.validate(SkScalarIsFinite(fScale));
 }