Update page_action and browser_action docs to say that default_icon is optional not required.

BUG=None
TEST=None

Review URL: http://codereview.chromium.org/6340001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71976 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/browserAction.html

@@ -385,7 +385,7 @@ like this:
   "name": "My extension",
   ...
   <b>"browser_action": {
-    "default_icon": "images/icon19.png", <em>// <b>required</b></em>
+    "default_icon": "images/icon19.png", <em>// optional</em>
     "default_title": "Google Mail",      <em>// optional; shown in tooltip</em>
     "default_popup": "popup.html"        <em>// optional</em>
   }</b>,
@@ -395,8 +395,7 @@ like this:
 <h2 id="ui">Parts of the UI</h2>
 
 <p>
-A browser action must have an <a href="#icon">icon</a>.
-It can also have
+A browser action can have an <a href="#icon">icon</a>,
 a <a href="#tooltip">tooltip</a>,
 a <a href="#badge">badge</a>,
 and a <a href="#popups">popup</a>.

chrome/common/extensions/docs/pageAction.html

@@ -378,7 +378,7 @@ like this:
   "name": "My extension",
   ...
   <b>"page_action": {
-    "default_icon": "icons/foo.png", <em>// <b>required</b></em>
+    "default_icon": "icons/foo.png", <em>// optional</em>
     "default_title": "Do action",    <em>// optional; shown in tooltip</em>
     "default_popup": "popup.html"    <em>// optional</em>
   }</b>,
@@ -389,8 +389,8 @@ like this:
 
 <p>
 Like browser actions,
-page actions have an icon and
-can also have a tooltip and popup;
+page actions can have an icon,
+a tooltip, and popup;
 they can't have badges, however.
 In addition, page actions can appear and disappear.
 You can find information about icons, tooltips, and popups

chrome/common/extensions/docs/static/browserAction.html

@@ -47,7 +47,7 @@ like this:
   "name": "My extension",
   ...
   <b>"browser_action": {
-    "default_icon": "images/icon19.png", <em>// <b>required</b></em>
+    "default_icon": "images/icon19.png", <em>// optional</em>
     "default_title": "Google Mail",      <em>// optional; shown in tooltip</em>
     "default_popup": "popup.html"        <em>// optional</em>
   }</b>,
@@ -57,8 +57,7 @@ like this:
 <h2 id="ui">Parts of the UI</h2>
 
 <p>
-A browser action must have an <a href="#icon">icon</a>.
-It can also have
+A browser action can have an <a href="#icon">icon</a>,
 a <a href="#tooltip">tooltip</a>,
 a <a href="#badge">badge</a>,
 and a <a href="#popups">popup</a>.

chrome/common/extensions/docs/static/pageAction.html

@@ -46,7 +46,7 @@ like this:
   "name": "My extension",
   ...
   <b>"page_action": {
-    "default_icon": "icons/foo.png", <em>// <b>required</b></em>
+    "default_icon": "icons/foo.png", <em>// optional</em>
     "default_title": "Do action",    <em>// optional; shown in tooltip</em>
     "default_popup": "popup.html"    <em>// optional</em>
   }</b>,
@@ -57,8 +57,8 @@ like this:
 
 <p>
 Like browser actions,
-page actions have an icon and
-can also have a tooltip and popup;
+page actions can have an icon,
+a tooltip, and popup;
 they can't have badges, however.
 In addition, page actions can appear and disappear.
 You can find information about icons, tooltips, and popups