Image filters: change applyCropRect() to take a src rect.

src/effects/SkDropShadowImageFilter.cpp

Index: src/effects/SkDropShadowImageFilter.cpp
diff --git a/src/effects/SkDropShadowImageFilter.cpp b/src/effects/SkDropShadowImageFilter.cpp
index eb05cf09eca99dfdbf0e381050fb6ae1b0074a42..5f8736f3a597049870962a1085b97325f731f619 100644
--- a/src/effects/SkDropShadowImageFilter.cpp
+++ b/src/effects/SkDropShadowImageFilter.cpp
@@ -62,8 +62,10 @@ bool SkDropShadowImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& source
     if (!this->filterInput(0, proxy, source, ctx, &src, &srcOffset))
         return false;
 
+    SkIRect srcBounds = src.bounds();
+    srcBounds.offset(srcOffset);
     SkIRect bounds;
-    if (!this->applyCropRect(ctx, src, srcOffset, &bounds)) {
+    if (!this->applyCropRect(ctx, srcBounds, &bounds)) {
         return false;
     }