build: [gn] centralize GN args under build/args/*.gn

Devs can still locally override or add settings by adding lines after
the `import` statement in args.gn.

This will help make sure that everyone has a common set of build args,
and will allow us to update everyone's build args in git.

.circleci/config.yml

@@ -354,17 +354,7 @@ jobs:
             echo 'export SCCACHE_WRAPPER="'`pwd`'/libchromiumcontent/tools/sccache/aad2120/linux/sccache"' >> $BASH_ENV
             echo 'export CHROMIUM_BUILDTOOLS_PATH=`pwd`/buildtools' >> $BASH_ENV
             source $BASH_ENV
-            mkdir out/Default
+            gn gen out/Default --args='import("//electron/build/args/debug.gn")'
-            cat > out/Default/args.gn <<-EOF
-            cc_wrapper = "$SCCACHE_WRAPPER"
-            root_extra_deps = [ "//electron" ]
-            is_electron_build = true
-            is_component_build = true
-            use_jumbo_build = true
-            v8_promise_internal_field_count = 1
-            v8_typed_array_max_size_in_heap = 0
-            EOF
-            gn gen out/Default
       - run:
           name: Ninja build
           command: |

build/args/all.gn

@@ -0,0 +1,10 @@
+is_electron_build = true
+is_electron_gn_build = true
+root_extra_deps = [ "//electron" ]
+
+v8_promise_internal_field_count = 1
+v8_typed_array_max_size_in_heap = 0
+
+enable_widevine = true
+proprietary_codecs = true
+ffmpeg_branding = "Chrome"

build/args/debug.gn

@@ -0,0 +1,4 @@
+import("all.gn")
+is_debug = true
+is_component_build = true
+use_jumbo_build = true

build/args/release.gn

@@ -0,0 +1,4 @@
+import("all.gn")
+is_component_build = false
+is_official_build = true
+is_component_ffmpeg = true

docs/development/build-instructions-gn.md

@@ -38,7 +38,7 @@ $ gclient sync --with_branch_heads --with_tags
 ```sh
 $ cd src
 $ export CHROMIUM_BUILDTOOLS_PATH=`pwd`/buildtools
-$ gn gen out/Default --args='root_extra_deps=["//electron"] is_electron_build=true is_component_build=true use_jumbo_build=true v8_promise_internal_field_count=1 v8_typed_array_max_size_in_heap=0'
+$ gn gen out/Default --args='import("//electron/build/args/debug.gn")'
 ```
 
 This will generate all the ninja files needed for the build. You shouldn't have