Add GrDirectContext arg to SkImage::readPixels

Note: The polarity of the staging flag is inverted from usual because
a G3 dependency with no SkUserConfig.h relies on the legacy API.

Once this lands, we will migrate them and others, then remove the
staging API. The inverted staging flag is kind of nice, actually - I may
use that pattern in the future. It means less total CLs and it's just as
easy to flip the bit on or off during debugging.

Bug: skia:104662
Change-Id: I48cba1eeae3e2e6f79918c6d243e0666e68ec71b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310656
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
diff --git a/tests/EncodeTest.cpp b/tests/EncodeTest.cpp
index 1785c18..c4a8b42 100644
--- a/tests/EncodeTest.cpp
+++ b/tests/EncodeTest.cpp
@@ -159,7 +159,7 @@
 
             SkBitmap bm;
             bm.allocPixels(info);
-            if (!surface->makeImageSnapshot()->readPixels(bm.pixmap(), 0, 0)) {
+            if (!surface->makeImageSnapshot()->readPixels(nullptr, bm.pixmap(), 0, 0)) {
                 ERRORF(r, "failed to readPixels! ct: %i\tat: %i\n", ct, at);
                 continue;
             }