Bug 1352726 - Ensure missing fields dont halt theming. r=sebastian

mobile/android/base/java/org/mozilla/gecko/webapps/WebAppActivity.java

@@ -156,7 +156,7 @@ public class WebAppActivity extends GeckoApp {
         try {
             final File manifestFile = new File(manifestPath);
             final JSONObject manifest = FileUtils.readJSONObjectFromFile(manifestFile);
-            final JSONObject manifestField = (JSONObject) manifest.get("manifest");
+            final JSONObject manifestField = manifest.getJSONObject("manifest");
             final Integer color = readColorFromManifest(manifestField);
             final String name = readNameFromManifest(manifestField);
             final Bitmap icon = readIconFromManifest(manifest);
@@ -180,27 +180,27 @@ public class WebAppActivity extends GeckoApp {
         }
     }
 
-    private Integer readColorFromManifest(JSONObject manifest) throws JSONException {
-        final String colorStr = (String) manifest.get("theme_color");
+    private Integer readColorFromManifest(JSONObject manifest) {
+        final String colorStr = manifest.optString("theme_color", null);
         if (colorStr != null) {
             return ColorUtil.parseStringColor(colorStr);
         }
         return null;
     }
 
-    private String readNameFromManifest(JSONObject manifest) throws JSONException {
-        String name = (String) manifest.get("name");
+    private String readNameFromManifest(JSONObject manifest) {
+        String name = manifest.optString("name", null);
         if (name == null) {
-            name = (String) manifest.get("short_name");
+            name = manifest.optString("short_name", null);
         }
         if (name == null) {
-            name = (String) manifest.get("start_url");
+            name = manifest.optString("start_url", null);
         }
         return name;
     }
 
-    private Bitmap readIconFromManifest(JSONObject manifest) throws JSONException {
-        final String iconStr = (String) manifest.get("cached_icon");
+    private Bitmap readIconFromManifest(JSONObject manifest) {
+        final String iconStr = manifest.optString("cached_icon", null);
         if (iconStr != null) {
             return FaviconDecoder
                 .decodeDataURI(getContext(), iconStr)