[Android] Add the @interface JavascriptInterface.

This annotation is used for XWalkView.addJavascriptInterface. This
is for security check so all Java methods called by JavaScript code
should be marked with this annotation.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1596
Revert "[Android] Add xwalk_core_sample_apk to xwalk_builder"

This reverts commit 5c52d2d319a221130e142798d889452209b23a69.

This commit will break the build when clean build.
Need further investigation about gyp dependency.
Merge pull request #1876 from yongsheng/fix1596

[Android] Add the @interface JavascriptInterface.
Merge pull request #1878 from kurli/build-fail

Revert "[Android] Add xwalk_core_sample_apk to xwalk_builder"