Documentation: Clarify that runtime.sendMessage does not notify itself

chrome/common/extensions/docs/templates/articles/nativeMessaging.html

 <h1>Native Messaging</h1>
 <p>
 Extensions and apps can exchange messages with native applications using an API
 that is similar to the other <a href="messaging">message passing APIs</a>.
 Native applications that support this feature must register a
 <em>native messaging host</em> that knows how to communicate with the extension.
 Chrome starts the host in a separate process and communicates with it using
 standard input and standard output streams.
 
 <h2 id="native-messaging-host">Native messaging host</h2>
@@ skipping 28 matching lines @@
     and dots. The name cannot start or end with a dot, and a dot cannot be
     followed by another dot.
     </td>
   </tr>
   <tr>
     <td><code>description</code></td>
     <td>Short application description.</td>
   </tr>
   <tr>
     <td><code>path</code></td>
-    <td>Path to the native messaging host binary. On Linux and OSX the path must
-    be absolute. On Windows it can be relative to the directory in which the
+    <td>Path to the native messaging host binary. On Windows the path must be
+    absolute, on Linux and OSX the path can be absolute or relative to the

[Devlin, 2016/08/23 16:30:34]

I don't think this is right - it looks like we do absolutify windows paths and
error out on posix.  We could probably tweak posix to handle relative, too, but
I think right now the documentation is accurate.

https://chromium.googlesource.com/chromium/src/+/c963c714c99f34bd80b392d9896c...

[robwu, 2016/08/24 06:49:42]

You're right, fixed!

+    directory in which the
     manifest file is located. The host process is started with the current
     directory set to the directory that contains the host binary. For example if
     this parameter is set to <code>C:\Application\nm_host.exe</code> then it
     will be started with current directory <code>C:\Application\</code>.</td>
   </tr>
   <tr>
     <td><code>type</code></td>
     <td>Type of the interface used to communicate with the native messaging
     host. Currently there is only one possible value for this parameter:
     <code>stdio</code>. It indicates that Chrome should use <code>stdin</code>
@@ skipping 153 matching lines @@
       Is the name spelled correctly in the extension and in the manifest file?
     <li>
       Is the manifest put in the right directory and with the correct name? See
       <a href="#native-messaging-host-location">native messaging host location</a>
       for the expected formats.
     <li>
       Is the manifest file in the correct format? In particular, is the JSON
       syntax correct and do the values match the definition of a
       <a href="#native-messaging-host-manifest">native messaging host manifest</a>?
     <li>
-      Does the file specified in <code>path</code> exist? On Windows, paths
-      may be relative, but on OS X and Linux, the paths must be absolute.
+      Does the file specified in <code>path</code> exist? On Linux and OS X the
+      path may be relative, but on Windows the path must be absolute.
   </ul>
 
   <dt>Native messaging host <em>host name</em> is not registered. (Windows-only)
   <dd>The native messaging host was not found in the Windows registry. Double-check
   using <code>regedit</code> whether the key was really created and matches the
   required format as documented at
   <a href="#native-messaging-host-location">native messaging host location</a>.
 
   <dt>Access to the specified native messaging host is forbidden.
   <dd>Is the extension's origin listed in <code>allowed_origins</code>?
@@ skipping 40 matching lines @@
 and
 <a href="https://developer.chrome.com/extensions/examples/api/nativeMessaging/host.zip">sample host</a>.
 
 Run <code>install_host.bat</code> (Windows) or
 <code>install_host.sh</code> (Linux / OS X) to install the native messaging
 host.
 Then <a href="getstarted#unpacked">load the app</a> and interact with the app.
 Run <code>uninstall_host.bat</code> or <code>uninstall_host.sh</code> to
 unregister the native messaging host when you are done.