Return NULL when building empty LayerRasterizer.

In SkLayerRasterizer::snapshotRasterizer() and ::detachRasterizer(),
if no layers have been added, do not attempt to create an
SkLayerRasterizer. Instead, return NULL.

This fixes an error when running tests on Android.

Update dox to state that NULL may be returned.

Add tests.

R=reed@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/313653006

1 files changed, 10 insertions, 1 deletions

diff --git a/src/effects/SkLayerRasterizer.cpp b/src/effects/SkLayerRasterizer.cpp
index ca611d5385..90fd59b585 100644
--- a/src/effects/SkLayerRasterizer.cpp
+++ b/src/effects/SkLayerRasterizer.cpp
@@ -213,12 +213,21 @@ void SkLayerRasterizer::Builder::addLayer(const SkPaint& paint, SkScalar dx,
 }
 
 SkLayerRasterizer* SkLayerRasterizer::Builder::detachRasterizer() {
-    SkLayerRasterizer* rasterizer = SkNEW_ARGS(SkLayerRasterizer, (fLayers));
+    SkLayerRasterizer* rasterizer;
+    if (0 == fLayers->count()) {
+        rasterizer = NULL;
+        SkDELETE(fLayers);
+    } else {
+        rasterizer = SkNEW_ARGS(SkLayerRasterizer, (fLayers));
+    }
     fLayers = NULL;
     return rasterizer;
 }
 
 SkLayerRasterizer* SkLayerRasterizer::Builder::snapshotRasterizer() const {
+    if (0 == fLayers->count()) {
+        return NULL;
+    }
     SkDeque* layers = SkNEW_ARGS(SkDeque, (sizeof(SkLayerRasterizer_Rec), fLayers->count()));
     SkDeque::F2BIter                iter(*fLayers);
     const SkLayerRasterizer_Rec*    recOrig;