Coverity: Fix pass by value errors in HostZoomMap::SetZoomLevel() function.

content/public/browser/host_zoom_map.h

Index: content/public/browser/host_zoom_map.h
diff --git a/content/public/browser/host_zoom_map.h b/content/public/browser/host_zoom_map.h
index d05e0d75c4008b4869e4bc21363a28a03a5bc16d..ed3c80d6b1f8abbf2128403ca69c5e5cf65d3f8d 100644
--- a/content/public/browser/host_zoom_map.h
+++ b/content/public/browser/host_zoom_map.h
@@ -45,7 +45,7 @@ class HostZoomMap {
   // from the saved preferences; otherwise the new value is written out.
   //
   // This should only be called on the UI thread.
-  virtual void SetZoomLevel(std::string host, double level) = 0;
+  virtual void SetZoomLevel(const std::string& host, double level) = 0;
 
   // Get/Set the default zoom level for pages that don't override it.
   virtual double GetDefaultZoomLevel() const = 0;