Move some zoom constants into the headers so we don't have to duplicate the values in plugins.

content/public/common/page_zoom.h

 // Copyright (c) 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.
 
 #ifndef CONTENT_PUBLIC_COMMON_PAGE_ZOOM_H_
 #define CONTENT_PUBLIC_COMMON_PAGE_ZOOM_H_
 #pragma once
 
 #include "content/common/content_export.h"
 
 namespace content {
 
 // This enum is the parameter to various text/page zoom commands so we know
 // what the specific zoom command is.
 enum PageZoom {
   PAGE_ZOOM_OUT   = -1,
   PAGE_ZOOM_RESET = 0,
   PAGE_ZOOM_IN    = 1,
 };
 
 // The minimum zoom factor permitted for a page. This is an alternative to
 // WebView::minTextSizeMultiplier.
 CONTENT_EXPORT extern const double kMinimumZoomFactor;
 
 // The maximum zoom factor permitted for a page. This is an alternative to
 // WebView::maxTextSizeMultiplier.
 CONTENT_EXPORT extern const double kMaximumZoomFactor;
 
+// Epsilon value for comparing two floating-point zoom values. We don't use
+// std::numeric_limits<> because it is too precise for zoom values. Zoom
+// values lose precision due to factor/level conversions. A value of 0.001
+// is precise enough for zoom value comparisons.
+CONTENT_EXPORT extern const double kEpsilon;
+
 // Test if two zoom values (either zoom factors or zoom levels) should be
 // considered equal.
 CONTENT_EXPORT bool ZoomValuesEqual(double value_a, double value_b);
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_PAGE_ZOOM_H_