Update Mac build instructions with GN

docs/mac_build_instructions.md

Index: docs/mac_build_instructions.md
diff --git a/docs/mac_build_instructions.md b/docs/mac_build_instructions.md
index 818b2e3cc743af8032797dc9fe2f47851c87e3b8..a48f7cdc2d3d2a18b583a63ad05538645e482810 100644
--- a/docs/mac_build_instructions.md
+++ b/docs/mac_build_instructions.md
@@ -72,12 +72,13 @@ kill them first.
 Full rebuilds are about the same speed in Debug and Release, but linking is a
 lot faster in Release builds.
 
-Run
+Add
 
-    GYP_DEFINES=fastbuild=1 build/gyp_chromium
+    symbol_level=1
 
-to disable debug symbols altogether, this makes both full rebuilds and linking
-faster (at the cost of not getting symbolized backtraces in gdb).
+to your [GN](../tools/gn/docs/quick_start.md) config to disable debug symbols
+altogether. This makes both full rebuilds and linking faster (at the cost of
+not getting symbolized backtraces in gdb).
 
 You might also want to [install ccache](ccache_mac.md) to speed up the build.
 
@@ -131,45 +132,10 @@ Once you’re comfortable with building Chromium, check out
 [Contributing Code](http://dev.chromium.org/developers/contributing-code) for
 information about writing code for Chromium and contributing it.
 
-## Using Xcode-Ninja Hybrid
+## Using Xcode
 
-While using Xcode is unsupported, GYP supports a hybrid approach of using ninja
-for building, but Xcode for editing and driving compilation. Xcode can still be
-slow, but it runs fairly well even **with indexing enabled**.
-
-With hybrid builds, compilation is still handled by ninja, and can be run by the
-command line (e.g. ninja -C out/Debug chrome) or by choosing the chrome target
-in the hybrid workspace and choosing build.
-
-To use Xcode-Ninja Hybrid, set GYP\_GENERATORS like the following:
-
-```shell
-export GYP_GENERATORS="ninja,xcode-ninja"
-```
-
-Due to the way Xcode parses ninja output paths, it's also necessary to change
-the main gyp location to anything two directories deep. Otherwise Xcode build
-output will not be clickable.
-To make this change permanent, you can edit `chromium.gyp_env` (or create it if
-it does not exists) and define GYP\_GENERATOR\_FLAGS. In general, to use hybrid
-mode, your `chromium.gyp_env` could contain the following:
-
-```json
-{
-  "GYP_GENERATORS"     : "ninja,xcode-ninja",
-  "GYP_GENERATOR_FLAGS":
-      "xcode_project_version=3.2 " +
-      "xcode_ninja_main_gyp=src/build/ninja/all.ninja.gyp",
-}
-```
-
-After, generate the project files with:
-
-```shell
-gclient runhooks
-```
-
-And finally, open it:
+Use the `--ide="xcode"` when running `gn gen` to generate the workspace, then
+open it:
 
 ```shell
 open build/ninja/all.ninja.xcworkspace
@@ -182,13 +148,6 @@ Versions Browser". When this option is checked, Xcode adds
 `--NSDocumentRevisionsDebugMode YES` to the launch arguments, and the `YES` gets
 interpreted as a URL to open.
 
-If you want to limit the number of targets visible, which is known to improve
-Xcode performance, add `xcode_ninja_executable_target_pattern=%target%` where

[vabr (Chromium), 2016/08/09 13:13:40]

I suppose that this might still be needed, but not sure how it translates to GN.
Any ideas?

-`%target%` is a regular expression matching executable targets you'd like to
-include.
-
-To include non-executable targets, use `xcode_ninja_target_pattern=All_iOS`.

[vabr (Chromium), 2016/08/09 13:13:40]

Ditto.

-
 If you have problems building, join us in `#chromium` on `irc.freenode.net` and
 ask there. As mentioned above, be sure that the
 [waterfall](http://build.chromium.org/buildbot/waterfall/) is green and the tree