Disable zoom bubble for PDF extension.

components/ui/zoom/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("zoom") {
   sources = [
     "page_zoom.cc",
     "page_zoom.h",
     "page_zoom_constants.cc",
     "page_zoom_constants.h",
     "zoom_controller.cc",
     "zoom_controller.h",
     "zoom_event_manager.cc",
     "zoom_event_manager.h",
     "zoom_event_manager_observer.h",
     "zoom_observer.h",
   ]
 
   deps = [
     "//base",
     "//base:prefs",
     "//content/public/browser",
     "//content/public/common",
     "//ipc",
     "//net",
     "//url",
   ]
 }
 
+source_set("test_support") {
+  testonly = true
+  sources = [
+    "test/zoom_test_utils.cc",
+    "test/zoom_test_utils.h",
+  ]
+  deps = [
+    ":zoom",
+    "//base:base",
+    "//content/test:test_support",
+  ]
+}
+
 source_set("unit_tests") {
   testonly = true
   sources = [
     "page_zoom_unittests.cc",
   ]
   deps = [
     ":zoom",
     "//base:prefs",
     "//content/public/common",
     "//testing/gtest",
   ]
 }