[Android] Change the super class of XWalkRuntimeView to LinearLayout

Advertising extension, refer to
https://github.com/crosswalk-project/crosswalk-android-extensions/pull/25,
will insert the ad view, which cannot cover the HTML content. Currently, the
supper class of XWalkRuntimeView is FrameLayout, which isn't able to shrink
when a view is inserted. So it will be replaced by LinearLayout.
According to http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4.4_r1/android/widget/LinearLayout.java#1755 , the default layout will be [match_parent, wrap_content]. We need [match_parent, match_parent] here.