images with offset bitmap don't share genid

tests/image-bitmap.cpp

Index: tests/image-bitmap.cpp
diff --git a/tests/image-bitmap.cpp b/tests/image-bitmap.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..59ab3f72be978e40736e4784df695980349d2be5
--- /dev/null
+++ b/tests/image-bitmap.cpp
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Test.h"
+
+#include "SkBitmap.h"
+#include "SkImage.h"
+
+// https://bug.skia.org/5096
+// Test that when we make an image from a subset of a bitmap, that it
+// has a diff (ID, dimensions) from an image made from the entire
+// bitmap or a different subset of the image.
+DEF_TEST(ImageBitmapIdentity, r) {
+    SkBitmap bm, a, b;
+    bm.allocN32Pixels(32, 64);
+    bm.eraseColor(SK_ColorBLACK);
+    bm.setImmutable();
+    (void)bm.extractSubset(&a, SkIRect::MakeXYWH(0, 0, 32, 32));
+    (void)bm.extractSubset(&b, SkIRect::MakeXYWH(0, 32, 32, 32));
+    REPORTER_ASSERT(r, a.getGenerationID() == b.getGenerationID());
+    auto img = SkImage::MakeFromBitmap(bm);
+    auto imgA = SkImage::MakeFromBitmap(a);
+    auto imgB = SkImage::MakeFromBitmap(b);
+    REPORTER_ASSERT(r, img->uniqueID() == bm.getGenerationID());
+    REPORTER_ASSERT(r, img->uniqueID() != imgA->uniqueID());
+    REPORTER_ASSERT(r, img->uniqueID() != imgB->uniqueID());
+    REPORTER_ASSERT(r, imgA->uniqueID() != imgB->uniqueID());
+    REPORTER_ASSERT(r, imgA->uniqueID() != a.getGenerationID());
+    REPORTER_ASSERT(r, imgB->uniqueID() != b.getGenerationID());
+}