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

content/common/page_zoom.cc

Index: content/common/page_zoom.cc
===================================================================
--- content/common/page_zoom.cc	(revision 114285)
+++ content/common/page_zoom.cc	(working copy)
@@ -10,16 +10,10 @@
 
 const double kMinimumZoomFactor = 0.25;
 const double kMaximumZoomFactor = 5.0;
+const double kEpsilon = 0.001;
 
 bool ZoomValuesEqual(double value_a, double value_b) {
-  // 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.
-  const double epsilon = 0.001;
-
-  return (std::fabs(value_a - value_b) <= epsilon);
+  return (std::fabs(value_a - value_b) <= kEpsilon);
 }
 
 }  // namespace content
-