Link the browser chrome (elements) definitions

These are both unused definitions before this change:
https://w3c.github.io/webdriver/#dfn-browser-chrome
https://w3c.github.io/webdriver/#dfn-browser-chrome-element

Author: foolip

index.html

@@ -2937,7 +2937,7 @@ <h3><dfn>Back</dfn></h3>
 <p class=note>This command causes the browser to traverse
  one step backward in the <a>joint session history</a>
  of the <a>current top-level browsing context</a>.
- This is equivalent to pressing the back button in the browser chrome
+ This is equivalent to pressing the back button in the <a>browser chrome</a>
  or invoking <code>window.history.back</code>.
 
 <p>The <a>remote end steps</a> are:
@@ -2982,7 +2982,7 @@ <h3><dfn>Forward</dfn></h3>
 <p class=note>This command causes the browser
  to traverse one step forwards in the <a>joint session history</a>
  of the <a>current top-level browsing context</a>.
- This is equivalent to pressing the forward button in the browser chrome
+ This is equivalent to pressing the forward button in the <a>browser chrome</a>
  or invoking <code>window.history.forward</code>.
 
 <p>The <a>remote end steps</a> are:
@@ -3717,13 +3717,13 @@ <h3><dfn>Set Window Rect</dfn></h3>
    <li><p>Set the width, in <a>CSS pixels</a>,
     of the operating system window containing
     the <a>current top-level browsing context</a>,
-    including any browser chrome and externally drawn window decorations
+    including any <a>browser chrome</a> and externally drawn window decorations
     to a value that is as close as possible to <var>width</var>.
 
   <li><p>Set the height, in <a>CSS pixels</a>,
    of the operating system window containing
    the <a>current top-level browsing context</a>,
-   including any browser chrome and externally drawn window decorations
+   including any <a>browser chrome</a> and externally drawn window decorations
    to a value that is as close as possible to <var>height</var>.
 
    <aside class=note>
@@ -9466,7 +9466,7 @@ <h2>Security</h2>
  make an effort to visually distinguish
  a user agent session that is under control of WebDriver
  from those used for normal browsing sessions.
- This can be done through a browser chrome element
+ This can be done through a <a>browser chrome element</a>
  such as a “door hanger”,
  colorful decoration of the OS window,
  or some widget element that is prevalent in the window