Clear webapp storage when site data is cleared

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.java
index 37511a3ccab40c6e2f30e3e24c989cb5a3750a48..f9e7d44aa60a36b617ff5c0370cba7c1c0484f40 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.java
@@ -79,6 +79,17 @@ public class WebappDataStorage {
     }
 
     /**
+     * Deletes the data for a webapp by clearing all the information inside the SharedPreference
+     * file. This does NOT delete the file itself but the file is left empty.
+     * @param context  The context to read the SharedPreferences file.
+     * @param webappId The ID of the webapp being deleted.
+     */
+    static void deleteDataForWebapp(final Context context, final String webappId) {
+        assert !ThreadUtils.runningOnUiThread();
+        openSharedPreferences(context, webappId).edit().clear().commit();
+    }
+
+    /**
      * Sets the factory used to generate WebappDataStorage objects.
      */
     @VisibleForTesting
@@ -86,11 +97,15 @@ public class WebappDataStorage {
         sFactory = factory;
     }
 
-    protected WebappDataStorage(Context context, String webappId) {
-        mPreferences = context.getApplicationContext().getSharedPreferences(
+    private static SharedPreferences openSharedPreferences(Context context, String webappId) {
+        return context.getApplicationContext().getSharedPreferences(
                 SHARED_PREFS_FILE_PREFIX + webappId, Context.MODE_PRIVATE);
     }
 
+    protected WebappDataStorage(Context context, String webappId) {
+        mPreferences = openSharedPreferences(context, webappId);
+    }
+
     /*
      * Asynchronously retrieves the splash screen image associated with the
      * current web app.