ZoomController: manual mode SetZoom() should early-out.

components/ui/zoom/zoom_controller.cc

Index: components/ui/zoom/zoom_controller.cc
diff --git a/components/ui/zoom/zoom_controller.cc b/components/ui/zoom/zoom_controller.cc
index 1a68fe4434d5196f7683b80442a9403b98f9719f..b471b7e5bf865c013a4ffaf1cadec60c2b5ab639 100644
--- a/components/ui/zoom/zoom_controller.cc
+++ b/components/ui/zoom/zoom_controller.cc
@@ -95,6 +95,10 @@ 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)
+      return true;
+
     double old_zoom_level = zoom_level_;
     zoom_level_ = zoom_level;