Move the local _isSafari() into dom-util.ts

The isSafari() function was introduced in master by this commit [1]
and then cherry-picked straight to stable-3.2[2]. However, since the
dom-util.ts did not exist in 3.2, the function was added directly into
the gr-diff.js file. as a local method (_isSafari()).

When stable-3.2 was merge into stable-3.3, the _isSafari() method was
never replaced by the dom-utils.ts.

[1]https://gerrit-review.googlesource.com/c/gerrit/+/296582
[2]https://gerrit-review.googlesource.com/c/gerrit/+/297615

Change-Id: Id61a7f6614bcabb8fe1b701a659c8e2dc7f83f04

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts

@@ -58,6 +58,8 @@ import {PolymerDeepPropertyChange} from '@polymer/polymer/interfaces';
 // @ts-ignore
 import * as shadow from 'shadow-selection-polyfill/shadow.js';
 
+import {isSafari} from '../../../utils/dom-util';
+
 const NO_NEWLINE_BASE = 'No newline at end of base file.';
 const NO_NEWLINE_REVISION = 'No newline at end of revision file.';
 
@@ -361,7 +363,7 @@ export class GrDiff extends GestureEventListeners(
     // element. This takes the shadow DOM selection if one exists.
     return this.root instanceof ShadowRoot && this.root.getSelection
       ? this.root.getSelection()
-      : this._isSafari()
+      : isSafari()
       ? shadow.getRange(this.root)
       : document.getSelection();
   }
@@ -1074,13 +1076,6 @@ export class GrDiff extends GestureEventListeners(
       }
     }, 0);
   }
-
-  _isSafari() {
-    return (
-      /^((?!chrome|android).)*safari/i.test(navigator.userAgent) ||
-      (/iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream)
-    );
-  }
 }
 
 declare global {

polygerrit-ui/app/utils/dom-util.ts

@@ -253,3 +253,11 @@ export function getSharedApiEl(): JsApiService {
   }
   return _sharedApiEl;
 }
+
+// Whether the browser is Safari. Used for polyfilling unique browser behavior.
+export function isSafari() {
+  return (
+    /^((?!chrome|android).)*safari/i.test(navigator.userAgent) ||
+    (/iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream)
+  );
+}