Documentation: Add .gni and .mojom in Eclipse setup instructions.

docs/linux_eclipse_dev.md

 # Linux Eclipse Dev
 
 Eclipse can be used on Linux (and probably Windows and Mac) as an IDE for
 developing Chromium. It's unpolished, but here's what works:
 
 *   Editing code works well (especially if you're used to it or Visual Studio).
 *   Navigating around the code works well. There are multiple ways to do this
     (F3, control-click, outlines).
 *   Building works fairly well and it does a decent job of parsing errors so
     that you can click and jump to the problem spot.
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 In the Project Explorer on the left side:
 
 1.  Right-click on "src" and select "Properties..."
 1.  Open Resource > Resource Filters
 1.  Click "Add..."
 1.  Add the following filter:
     *   Include only
     *   Files, all children (recursive)
     *   Name matches
-        `.*\.(c|cc|cpp|h|mm|inl|idl|js|json|css|html|gyp|gypi|grd|grdp|gn)`
+        `.*\.(c|cc|cpp|h|mm|inl|idl|js|json|css|html|gyp|gypi|grd|grdp|gn|gni|mojom)`
         regular expression
 1.  Add another filter:
     *   Exclude all
     *   Folders
     *   Name matches `out_.*|\.git|\.svn|LayoutTests` regular expression
         *   If you aren't working on WebKit, adding `|WebKit` will remove more
             files
 1.  Click "OK"
 
 Don't exclude the primary "out" directory, as it contains generated header files
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 ### Additional tips
 
 1.  Mozilla's
     [Eclipse CDT guide](https://developer.mozilla.org/en-US/docs/Eclipse_CDT)
     is helpful:
 1.  For improved performance, I use medium-granularity projects (eg. one for
     WebKit/Source) instead of putting all of 'src/' in one project.
 1.  For working in Blink (which uses WebKit code style), feel free to use
     [this](https://drive.google.com/file/d/0B2LVVIKSxUVYM3R6U0tUa1dmY0U/view?usp=sharing)
     code-style formatter XML profile