Use ZoomValuesEqual() instead of ==.

Replace an unsafe comparison of zoom level values.

BUG=none

Review URL: https://codereview.chromium.org/1032503003

Cr-Commit-Position: refs/heads/master@{#321866}

components/ui/zoom/zoom_controller.cc

@@ -96,7 +96,7 @@ bool ZoomController::SetZoomLevelByClient(
   // Do not actually rescale the page in manual mode.
   if (zoom_mode_ == ZOOM_MODE_MANUAL) {
     // If the zoom level hasn't changed, early out to avoid sending an event.
-    if (zoom_level_ == zoom_level)
+    if (content::ZoomValuesEqual(zoom_level_, zoom_level))
       return true;
 
     double old_zoom_level = zoom_level_;