[android_webview] Use a fraction to calculate scroll offset.

cc/layers/layer_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/strings/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ skipping 983 matching lines @@
 void LayerImpl::SetScrollOffsetDelegate(
     LayerScrollOffsetDelegate* scroll_offset_delegate) {
   // Having both a scroll parent and a scroll offset delegate is unsupported.
   DCHECK(!scroll_parent_);
   if (!scroll_offset_delegate && scroll_offset_delegate_) {
     scroll_delta_ =
         scroll_offset_delegate_->GetTotalScrollOffset() - scroll_offset_;
   }
   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) {
   SetScrollOffsetAndDelta(scroll_offset, ScrollDelta());
 }
 
 void LayerImpl::SetScrollOffsetAndDelta(gfx::Vector2d scroll_offset,
                                         gfx::Vector2dF scroll_delta) {
   bool changed = false;
 
@@ skipping 65 matching lines @@
 
 void LayerImpl::DidBeginTracing() {}
 
 void LayerImpl::DidLoseOutputSurface() {}
 
 void LayerImpl::SetMaxScrollOffset(gfx::Vector2d max_scroll_offset) {
   if (max_scroll_offset_ == 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();
 }
 
 void LayerImpl::DidBecomeActive() {
   if (layer_tree_impl_->settings().scrollbar_animator ==
       LayerTreeSettings::NoAnimator) {
     return;
   }
 
@@ skipping 218 matching lines @@
 
 size_t LayerImpl::GPUMemoryUsageInBytes() const { return 0; }
 
 scoped_ptr<base::Value> LayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   AsValueInto(state.get());
   return state.PassAs<base::Value>();
 }
 
 }  // namespace cc