add thumbnails to the books example to make memory leaks easier to test

add_to_app/books/android_books/app/build.gradle

@@ -20,6 +20,7 @@ android {
         release {
             minifyEnabled false
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+            signingConfig debug.signingConfig
         }
     }
     compileOptions {

add_to_app/books/android_books/app/src/main/java/dev/flutter/example/books/MainActivity.kt

@@ -94,6 +94,9 @@ class MainActivity : AppCompatActivity() {
                 book.summary = volumeInfoJson.get("description").asString
                 book.publishDate = volumeInfoJson.get("publishedDate").asString
                 book.pageCount = volumeInfoJson.get("pageCount").asLong
+                val thumbnail = Api.Thumbnail()
+                thumbnail.url = volumeInfoJson.getAsJsonObject("imageLinks").get("thumbnail").asString
+                book.thumbnail = thumbnail
                 books.add(book)
             } catch (e: Exception) {
                 println("Failed to parse book:")