[android_webview] Use a fraction to calculate scroll offset.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index b0c5399d32e3a3fd06c1963eb585e671e52a6ca4..8a0d01898f57ac87c27bbd468b42bc2448cb5c1b 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -1001,8 +1001,10 @@ void LayerImpl::SetScrollOffsetDelegate(
   }
   gfx::Vector2dF total_offset = TotalScrollOffset();
   scroll_offset_delegate_ = scroll_offset_delegate;
-  if (scroll_offset_delegate_)
+  if (scroll_offset_delegate_) {
+    scroll_offset_delegate_->SetMaxScrollOffset(max_scroll_offset_);
     scroll_offset_delegate_->SetTotalScrollOffset(total_offset);
+  }
 }
 
 void LayerImpl::SetScrollOffset(gfx::Vector2d scroll_offset) {
@@ -1088,6 +1090,9 @@ void LayerImpl::SetMaxScrollOffset(gfx::Vector2d max_scroll_offset) {
     return;
   max_scroll_offset_ = max_scroll_offset;
 
+  if (scroll_offset_delegate_)
+    scroll_offset_delegate_->SetMaxScrollOffset(max_scroll_offset_);
+
   layer_tree_impl()->set_needs_update_draw_properties();
   UpdateScrollbarPositions();
 }