Make sure WebContents passed to chrome_page_zoom::Zoom() have a ZoomController.

chrome/browser/devtools/devtools_window.cc

Index: chrome/browser/devtools/devtools_window.cc
diff --git a/chrome/browser/devtools/devtools_window.cc b/chrome/browser/devtools/devtools_window.cc
index 0a14a7806499be7a575eab01142db3dea4ac04cc..e36c9f59e9bfeb4d3cfd1217607387f04a53a369 100644
--- a/chrome/browser/devtools/devtools_window.cc
+++ b/chrome/browser/devtools/devtools_window.cc
@@ -26,6 +26,7 @@
 #include "chrome/browser/ui/prefs/prefs_tab_helper.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/webui/devtools_ui.h"
+#include "chrome/browser/ui/zoom/zoom_controller.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/render_messages.h"
@@ -714,6 +715,9 @@ DevToolsWindow::DevToolsWindow(Profile* profile,
       DevToolsUIBindings::ApplyThemeToURL(profile, url));
   // Bindings take ownership over devtools as its delegate.
   bindings_->SetDelegate(this);
+  // DevTools uses chrome_page_zoom::Zoom(), so main_web_contents_ requires a
+  // ZoomController.
+  ZoomController::CreateForWebContents(main_web_contents_);
 
   g_instances.Get().push_back(this);