cc: Clamp the fixed thumb size to be at least zero.

cc/scrollbar_geometry_stub.cc

 // Copyright 2012 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/scrollbar_geometry_stub.h"
 
+#include <cmath>
+
 using WebKit::WebRect;
 using WebKit::WebScrollbar;
 using WebKit::WebScrollbarThemeGeometry;
 
 namespace cc {
 
 ScrollbarGeometryStub::ScrollbarGeometryStub(scoped_ptr<WebScrollbarThemeGeometry> geometry)
     : m_geometry(geometry.Pass())
 {
 }
 
 ScrollbarGeometryStub::~ScrollbarGeometryStub()
 {
 }
 
 WebScrollbarThemeGeometry* ScrollbarGeometryStub::clone() const
 {
     return m_geometry->clone();
 }
 
 int ScrollbarGeometryStub::thumbPosition(WebScrollbar* scrollbar)
 {
     return m_geometry->thumbPosition(scrollbar);
 }
 
 int ScrollbarGeometryStub::thumbLength(WebScrollbar* scrollbar)
 {
-    return m_geometry->thumbLength(scrollbar);
+    return std::max(0, m_geometry->thumbLength(scrollbar));
 }
 
 int ScrollbarGeometryStub::trackPosition(WebScrollbar* scrollbar)
 {
     return m_geometry->trackPosition(scrollbar);
 }
 
 int ScrollbarGeometryStub::trackLength(WebScrollbar* scrollbar)
 {
     return m_geometry->trackLength(scrollbar);
@@ skipping 53 matching lines @@
 {
     return m_geometry->constrainTrackRectToTrackPieces(scrollbar, rect);
 }
 
 void ScrollbarGeometryStub::splitTrack(WebScrollbar* scrollbar, const WebRect& unconstrainedTrackRect, WebRect& beforeThumbRect, WebRect& thumbRect, WebRect& afterThumbRect)
 {
     m_geometry->splitTrack(scrollbar, unconstrainedTrackRect, beforeThumbRect, thumbRect, afterThumbRect);
 }
 
 }  // namespace cc