Fix b/10456377.

Use WebView.getContentHeight() to compute the
additional bottom border rather than the container's
height which never actually expands.

Change-Id: Ifad68a93043ec50e75720bc53e57d830cd2abdf9
diff --git a/src/com/android/mail/browse/ConversationContainer.java b/src/com/android/mail/browse/ConversationContainer.java
index 38bfb17..b705dba 100644
--- a/src/com/android/mail/browse/ConversationContainer.java
+++ b/src/com/android/mail/browse/ConversationContainer.java
@@ -558,7 +558,7 @@
      */
     private void positionAdditionalBottomBorder() {
         final int lastBottom = mAdditionalBottomBorderOverlayTop;
-        final int containerHeight = getHeight();
+        final int containerHeight = webPxToScreenPx(mWebView.getContentHeight());
         final int speculativeHeight = containerHeight - lastBottom;
         if (speculativeHeight > 0) {
             if (mAdditionalBottomBorder == null) {