feat: priority use document.baseURI to replace window.location

- respect `<base>` tag

in case: when view page cache, search engine will inject `<base>` tag to current html
but `window.location` is still `webcache.googleusercontent.com/search?q=cache:...`

in most situation `baseURI` is equal to `window.location`

src/history/base.js

@@ -3,7 +3,6 @@
 import { _Vue } from '../install'
 import type Router from '../index'
 import { warn } from '../util/warn'
-import { inBrowser } from '../util/dom'
 import { runQueue } from '../util/async'
 import { START, isSameRoute } from '../util/route'
 
@@ -189,13 +188,7 @@ export class History {
 
 function normalizeBase (base: ?string): string {
   if (!base) {
-    if (inBrowser) {
-      // respect <base> tag
-      const baseEl = document.querySelector('base')
-      base = (baseEl && baseEl.getAttribute('href')) || '/'
-    } else {
-      base = '/'
-    }
+    base = '/'
   }
   // make sure there's the starting slash
   if (base.charAt(0) !== '/') {

src/history/html5.js

@@ -61,6 +61,13 @@ export class HTML5History extends History {
 
 export function getLocation (base: string): string {
   let path = window.location.pathname
+  const baseURI = document.baseURI
+  if (baseURI) {
+    const a = document.createElement('a')
+    a.href = baseURI
+    path = a.pathname
+  }
+
   if (base && path.indexOf(base) === 0) {
     path = path.slice(base.length)
   }