Revert "Remove Android-specific SK_SUPPORT_LEGACY_IMG_SNAPSHOT flag"

This reverts commit c3efe67856.

Reason for revert: RenderNodeDrawableTests.cpp

Original change's description:
> Remove Android-specific SK_SUPPORT_LEGACY_IMG_SNAPSHOT flag
> 
> Android has been updated to use the new signature so this should no longer be needed
> 
> Change-Id: Id745191e815381d032aba6a49bf4baf9c53b2385
> Reviewed-on: https://skia-review.googlesource.com/9985
> Reviewed-by: Derek Sollenberger <djsollen@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>
> 

TBR=djsollen@google.com,robertphillips@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I0211342b237373fe40d205bb18bbef5efce56bf3
Reviewed-on: https://skia-review.googlesource.com/9946
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>

gn/android_framework_defines.gni

@@ -16,4 +16,5 @@ android_framework_defines = [
   "SK_SUPPORT_LEGACY_SHADER_ISABITMAP",
   "SK_SUPPORT_LEGACY_EMBOSSMASKFILTER",
   "SK_SUPPORT_LEGACY_CANVAS_HELPERS",
+  "SK_SUPPORT_LEGACY_IMG_SNAPSHOT",
 ]

src/image/SkSurface_Base.h

@@ -43,7 +43,16 @@ public:
      *  must faithfully represent the current contents, even if the surface
      *  is changed after this called (e.g. it is drawn to via its canvas).
      */
+#ifdef SK_SUPPORT_LEGACY_IMG_SNAPSHOT
+    // This entry point is never called but is just here so Android unit tests will compile
+    virtual sk_sp<SkImage> onNewImageSnapshot(SkBudgeted) { return nullptr; }
+
+    // This entry point should be pure virtual. It has a default implementation so Android
+    // unit tests will compile.
+    virtual sk_sp<SkImage> onNewImageSnapshot() { return nullptr; }
+#else
     virtual sk_sp<SkImage> onNewImageSnapshot() = 0;
+#endif
 
     /**
      *  Default implementation: