Create gn arg templates for use with blimp builds. Update build doc.

blimp/docs/build.md

Index: blimp/docs/build.md
diff --git a/blimp/docs/build.md b/blimp/docs/build.md
index 425ad370b8513e47169b4033dc961a8658d8c4f7..aaa7bfd3491c741c7a8a2ac42a394c7f38fb2610 100644
--- a/blimp/docs/build.md
+++ b/blimp/docs/build.md
@@ -12,18 +12,8 @@ Create an out-directory and set the GN args:
 
 ```bash
 mkdir -p out-android/Debug
-gn args out-android/Debug
-```
-
-This will bring up an editor, where you can type in the following:
-
-```bash
-target_os = "android"
-is_debug = true
-is_clang = true
-is_component_build = true
-symbol_level = 1  # Use -g1 instead of -g2
-use_goma = true
+echo "import(\"//build/args/blimp_client.gn\")" > out-android/Debug/args.gn
+gn gen out-android/Debug
 ```
 
 To build:
@@ -45,28 +35,15 @@ Create another out-directory and set the GN args. Note, when building to run
 inside a [Docker container](container.md) you'll need to set the target_os to "chromeos":
 
 ```bash
-mkdir -p out-chromeos/Debug
-gn args out-chromeos/Debug
-```
-
-This will bring an editor, where you can type in the following:
-
-```bash
-target_os = "chromeos"
-is_debug = true
-is_clang = true
-symbol_level = 1  # Use -g1 instead of -g2
-use_goma = true
-use_aura = true
-use_ozone = true
-use_alsa = false
-use_pulseaudio = false
+mkdir -p out-docker/Debug
+echo "import(\"//build/args/blimp_engine_containerized.gn\")" > out-docker/Debug/args.gn
+gn gen out-docker/Debug
 ```
 
 To build:
 
 ```bash
-ninja -C out-chromeos/Debug blimp
+ninja -C out-docker/Debug blimp
 ```
 
 ## "Bare" engine, no Docker container
@@ -75,19 +52,8 @@ Create another out-directory and set the GN args:
 
 ```bash
 mkdir -p out-linux/Debug
-gn args out-linux/Debug
-```
-
-This will bring an editor, where you can type in the following:
-
-```bash
-is_debug = true
-is_clang = true
-is_component_build = true
-symbol_level = 1  # Use -g1 instead of -g2
-use_goma = true
-use_aura = true
-use_ozone = true
+echo "import(\"//build/args/blimp_engine.gn\")" > out-linux/Debug/args.gn
+gn gen out-linux/Debug
 ```
 
 To build: