Fix viewer on Android

We need libandroid in all scenarios, not just vulkan.
Also, the logic for making an off-screen surface was
wrong - causing us to try and make one in legacy mode.

BUG=skia:

Change-Id: I5ef2e3e2d46de96e9824f6a12a13f6310ea04f81
Reviewed-on: https://skia-review.googlesource.com/8252
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index d0f415d..656ed5e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1376,6 +1376,7 @@
           "tools/viewer/sk_app/android/main_android.cpp",
           "tools/viewer/sk_app/android/surface_glue_android.cpp",
         ]
+        libs += [ "android" ]
       } else if (is_linux) {
         sources += [
           "tools/viewer/sk_app/unix/GLWindowContext_unix.cpp",
@@ -1404,7 +1405,6 @@
         if (is_android) {
           sources +=
               [ "tools/viewer/sk_app/android/VulkanWindowContext_android.cpp" ]
-          libs += [ "android" ]
         } else if (is_linux) {
           sources += [ "tools/viewer/sk_app/unix/VulkanWindowContext_unix.cpp" ]
           libs += [ "X11-xcb" ]