Make an Android-specific copy of Skia's Null GL interface

This functionality has been removed from Skia, but is still being used
by HWUI's NullGlesDriver for unit tests. Making a local copy gets tests
passing (so that rolling can resume).

Test: hwui_unit_tests still pass
Change-Id: I16b65af58eaeca5a39df89d1542760b652d8b0d5
diff --git a/libs/hwui/debug/NullGlesDriver.cpp b/libs/hwui/debug/NullGlesDriver.cpp
index 212b242..f27adf0 100644
--- a/libs/hwui/debug/NullGlesDriver.cpp
+++ b/libs/hwui/debug/NullGlesDriver.cpp
@@ -20,8 +20,10 @@
 namespace uirenderer {
 namespace debug {
 
+extern const GrGLInterface* CreateNullSkiaInterface();
+
 sk_sp<const GrGLInterface> NullGlesDriver::getSkiaInterface() {
-    sk_sp<const GrGLInterface> skiaInterface(GrGLCreateNullInterface());
+    sk_sp<const GrGLInterface> skiaInterface(CreateNullSkiaInterface());
     return skiaInterface;
 }