adding preabandon flag to DM

BUG=skia:

Review URL: https://codereview.chromium.org/929243004
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index d2b8bc3..0f6599d 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -1130,6 +1130,9 @@
             fTextureAccess.reset(fAtlas->getTexture(), params);
         } else {
             SkAutoTUnref<GrTexture> texture(GrRefCachedBitmapTexture(ctx, bitmap, &params));
+            if (!texture) {
+                return;
+            }
             fCoordTransform.reset(kCoordSet, matrix, texture, params.filterMode());
             fTextureAccess.reset(texture, params);
             fYCoord = SK_ScalarHalf;