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

content/public/common/page_zoom.h

Index: content/public/common/page_zoom.h
===================================================================
--- content/public/common/page_zoom.h	(revision 114285)
+++ content/public/common/page_zoom.h	(working copy)
@@ -26,6 +26,12 @@
 // 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);