Update Linux eclipse docs for GN

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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 ### Optional: Accurate symbol information
 
 If setup properly, Eclipse can do a great job of semantic navigation of C++ code
 (showing type hierarchies, finding all references to a particular method even
 when other classes have methods of the same name, etc.). But doing this well
 requires the Eclipse knows correct include paths and pre-processor definitions.
 After fighting with with a number of approaches, I've found the below to work
 best for me.
 
-*The instrcutions below are out-of-date since it references GYP. Please see
-`gn help gen` for how to generate an Eclipse CDT file in GN. If you use
-Eclipse and make it work, please update this documentation.*
-
 1.  From a shell in your src directory, run
-    `GYP_GENERATORS=ninja,eclipse build/gyp_chromium`
-    1.  This generates <project root>/out/Debug/eclipse-cdt-settings.xml which
+    `gn gen --ide=eclipse out/Debug_gn/' (replacing Debug_gn with the output directory you normally use when building).
+    1.  This generates <project root>/out/Debug_gn/eclipse-cdt-settings.xml which
         is used below.
     1.  This creates a single list of include directories and preprocessor
         definitions to be used for all source files, and so is a little
         inaccurate. Here are some tips for compensating for the limitations:
-        1.  Use `-R <target>` to restrict the output to considering only certain
-            targets (avoiding unnecessary includes that are likely to cause
-            trouble). Eg. for a blink project, use `-R blink`.

[Dirk Pranke, 2016/07/06 18:19:26]

You might replace this with a mention of the --filters arg, which does roughly
the same thing (though it also includes dependencies).

         1.  If you care about blink, move 'third\_party/Webkit/Source' to the
             top of the list to better resolve ambiguous include paths (eg.
             `config.h`).
 1.  Import paths and symbols
     1.  Right click on the project and select Properties > C/C++ General > Paths
         and Symbols
     1.  Click Restore Defaults to clear any old settings
     1.  Click Import Settings... > Browse... and select
         `<project root>/out/Debug/eclipse-cdt-settings.xml`
     1.  Click the Finish button.  The entire preferences dialog should go away.
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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