change write-image to use pipeverbs like everyone else, and add test

tests/PipeTest.cpp

Index: tests/PipeTest.cpp
diff --git a/tests/PipeTest.cpp b/tests/PipeTest.cpp
index f345debb8ca46ba012350137059f516fd5219163..7f42071a7564cf6548b2aeec286f83f50c8f60be 100644
--- a/tests/PipeTest.cpp
+++ b/tests/PipeTest.cpp
@@ -49,7 +49,7 @@ static bool deep_equal(SkImage* a, SkImage* b) {
     return true;
 }
 
-DEF_TEST(Pipe_image, reporter) {
+DEF_TEST(Pipe_image_draw_first, reporter) {
     sk_sp<SkImage> img = GetResourceAsImage("mandrill_128.png");
     SkASSERT(img.get());
 
@@ -86,3 +86,30 @@ DEF_TEST(Pipe_image, reporter) {
     auto img2 = drain_as_image(&deserializer, &stream);
     REPORTER_ASSERT(reporter, img1.get() == img2.get());
 }
+
+DEF_TEST(Pipe_image_draw_second, reporter) {
+    sk_sp<SkImage> img = GetResourceAsImage("mandrill_128.png");
+    SkASSERT(img.get());
+
+    SkPipeSerializer serializer;
+    SkPipeDeserializer deserializer;
+    SkDynamicMemoryWStream stream;
+
+    serializer.write(img.get(), &stream);
+    size_t offset0 = stream.bytesWritten();
+    REPORTER_ASSERT(reporter, offset0 > 100);   // the raw image must be sorta big
+    drain_as_image(&deserializer, &stream);
+
+    // The 2nd image should be nice and small
+    serializer.write(img.get(), &stream);
+    size_t offset1 = stream.bytesWritten();
+    REPORTER_ASSERT(reporter, offset1 <= 32);
+    drain_as_image(&deserializer, &stream);
+
+    // Now try drawing the image, it should also be small
+    SkCanvas* wc = serializer.beginWrite(SkRect::MakeWH(100, 100), &stream);
+    wc->drawImage(img, 0, 0, nullptr);
+    serializer.endWrite();
+    size_t offset2 = stream.bytesWritten();
+    REPORTER_ASSERT(reporter, offset2 <= 32);
+}