libviewer.so on Android, delete hello_skia_app

This spins off parts of 5620 to bake while we work through how to do the rest of libviewer.so -> viewer.apk.

Change-Id: I1cbf135cc952eeb7593e80a5a752dcadaa2dbb00
Reviewed-on: https://skia-review.googlesource.com/5656
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 1ee4d60..c687ded 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1311,8 +1311,8 @@
     testonly = true
   }
 
-  if (skia_enable_gpu && (is_linux || is_win || is_mac)) {
-    executable("viewer") {
+  if (skia_enable_gpu && (is_android || is_linux || is_win || is_mac)) {
+    source_set("viewer_sources") {
       sources = [
         "tools/viewer/GMSlide.cpp",
         "tools/viewer/ImageSlide.cpp",
@@ -1389,6 +1389,22 @@
       }
       testonly = true
     }
+
+    if (is_android) {
+      shared_library("libviewer") {
+        deps = [
+          ":viewer_sources",
+        ]
+        testonly = true
+      }
+    } else {
+      executable("viewer") {
+        deps = [
+          ":viewer_sources",
+        ]
+        testonly = true
+      }
+    }
   }
 
   if (skia_enable_gpu) {