Use computeVerticalScrollRange() to find the bottom
of the page as mContentHeight is not in the view system.

Fix http://b/issue?id=2251909
diff --git a/core/java/android/webkit/WebView.java b/core/java/android/webkit/WebView.java
index 06e3e73..142774f 100644
--- a/core/java/android/webkit/WebView.java
+++ b/core/java/android/webkit/WebView.java
@@ -1525,7 +1525,7 @@
         }
         nativeClearCursor(); // start next trackball movement from page edge
         if (bottom) {
-            return pinScrollTo(mScrollX, mContentHeight, true, 0);
+            return pinScrollTo(mScrollX, computeVerticalScrollRange(), true, 0);
         }
         // Page down.
         int h = getHeight();