参考文章：
1、怎样的Flutter Engine定制流程，才能实现真正“开箱即用”？-阿里云开发者社区
所需环境
1、git基础命令。
2、可访问外网。
3、Python 2.7。
4、gclient，这是chromium所使用的一个源码库管理的工具，可以很好的管理源码以及对应的依赖，通过gclinet我们可以获取所有的编译需要的源码和依赖。
5、ninja ，编译工具，负责最终的编译工作。
6、gn ****，负责生成 ninja编译需要的build文件，特别像Flutter这种跨多种操作系统平台跨多种CPU架构的，就需要通过gn生成很多套不同的ninja build文件。
开始编译
1、创建一个工作目录，比如一个名为engine的目录。
2、目录下创建一个gclient的配置文件.gclient, 此配置文件的语法可以参见 chromium.googlesource.com/chromium/to…
solutions = [
{
"managed": False,
"name": "src/flutter",
"url": "git@github.com:BuildAndRelease/engine.git",
"custom_deps": {
'src/third_party/skia':"git@github.com:BuildAndRelease/skia.git@8230258098305e6a6b1f5578f4ea8816c95bc772"
},
"deps_file": "DEPS",
"safesync_url": "",
},
]
3、下载engine源码
engine目录执行 gclient sync，这个步骤比较耗时，不要提前手动kill掉进程。第一次gclient sync 执行完成了，engine/src/flutter为Flutter Engine源码的位置，我们需要手动切换到对应的版本分支，然后再次执行gclinet sync对此版本的依赖重新同步下，此次执行会比首次执行快很多。
4、检出对应flutter engine版本
首先获取我们当前使用的Flutter版本的提交记录。
cat /当前flutter的路径/bin/internal/engine.version
得到v1.0.0版本的提交记录为
7375a0f414bde4bc941e623482221db2fc8c4ab5n
然后将源码同步到上述提交记录上，执行如下命令然后约等待10分钟。
cd /path/to/engine/src/flutter
git reset --hard 3459eb24361807fb186953a864cf890fa8e9d26a
gclient sync --with_branch_heads --with_tags --verbose
之后即可进行编译。
5、构建引擎产物
cd至 engine/src目录
cd /path/to/engine/src/
./flutter/tools/gn --android --android-cpu arm64 --runtime-mode=release
ninja -C out/android_release_arm64
同理你可以按照如上命令构造flutter其他平台，其他CPU架构的引擎产物。
usage: gn [-h] [--unoptimized]
[--runtime-mode {debug,profile,release,jit_release}] [--interpreter]
[--dart-debug] [--no-dart-version-git-info] [--full-dart-debug]
[--target-os {android,ios,linux,fuchsia,win,winuwp}] [--android]
[--android-cpu {arm,x64,x86,arm64}] [--ios] [--ios-cpu {arm,arm64}]
[--simulator] [--fuchsia] [--fuchsia-legacy] [--no-fuchsia-legacy]
[--winuwp] [--linux-cpu {x64,x86,arm64,arm}]
[--fuchsia-cpu {x64,arm64}] [--windows-cpu {x64,arm64}]
[--simulator-cpu {x64,arm64}] [--arm-float-abi {hard,soft,softfp}]
[--goma] [--no-goma] [--xcode-symlinks] [--no-xcode-symlinks]
[--depot-tools DEPOT_TOOLS] [--lto] [--no-lto] [--clang]
[--no-clang] [--clang-static-analyzer] [--no-clang-static-analyzer]
[--target-sysroot TARGET_SYSROOT]
[--target-toolchain TARGET_TOOLCHAIN]
[--target-triple TARGET_TRIPLE]
[--operator-new-alignment OPERATOR_NEW_ALIGNMENT]
[--macos-enable-metal] [--enable-vulkan] [--enable-fontconfig]
[--enable-vulkan-validation-layers] [--enable-skshaper]
[--no-enable-skshaper] [--always-use-skshaper]
[--embedder-for-target] [--coverage] [--out-dir OUT_DIR]
[--full-dart-sdk] [--no-full-dart-sdk] [--ide IDE]
[--disable-desktop-embeddings] [--build-glfw-shell]
[--no-build-glfw-shell] [--bitcode] [--stripped] [--no-stripped]
[--asan] [--lsan] [--msan] [--tsan] [--ubsan]
optional arguments:
-h, --help show this help message and exit
--unoptimized
--runtime-mode {debug,profile,release,jit_release}
--interpreter
--dart-debug Enables assertions in the Dart VM. Does not affect
optimization levels. If you need to disable
optimizations in Dart, use --full-dart-debug
--no-dart-version-git-info
Set by default; if unset, turns off the dart SDK git
hash check
--full-dart-debug Implies --dart-debug and also disables optimizations
in the Dart VM making it easier to step through VM
code in the debugger.
--target-os {android,ios,linux,fuchsia,win,winuwp}
--android
--android-cpu {arm,x64,x86,arm64}
--ios
--ios-cpu {arm,arm64}
--simulator
--fuchsia
--fuchsia-legacy
--no-fuchsia-legacy
--winuwp
--linux-cpu {x64,x86,arm64,arm}
--fuchsia-cpu {x64,arm64}
--windows-cpu {x64,arm64}
--simulator-cpu {x64,arm64}
--arm-float-abi {hard,soft,softfp}
--goma
--no-goma
--xcode-symlinks Set to true for builds targetting macOS or iOS when
using goma. If set, symlinks to the Xcode provided
sysroot and SDKs will be created in a generated
folder, which will avoid potential backend errors in
Fuchsia RBE. Instead of specifying the flag on each
invocation the FLUTTER_GOMA_CREATE_XCODE_SYMLINKS
environment variable may be set to 1 to achieve the
same effect.
--no-xcode-symlinks
--depot-tools DEPOT_TOOLS
Depot tools provides an alternative location for
gomacc in /path/to/depot_tools/.cipd_bin
--lto
--no-lto
--clang
--no-clang
--clang-static-analyzer
--no-clang-static-analyzer
--target-sysroot TARGET_SYSROOT
--target-toolchain TARGET_TOOLCHAIN
--target-triple TARGET_TRIPLE
--operator-new-alignment OPERATOR_NEW_ALIGNMENT
--macos-enable-metal
--enable-vulkan
--enable-fontconfig
--enable-vulkan-validation-layers
--enable-skshaper
--no-enable-skshaper
--always-use-skshaper
--embedder-for-target
--coverage
--out-dir OUT_DIR
--full-dart-sdk include trained dart2js and dartdevc snapshots. Enable
only on steps that create an SDK
--no-full-dart-sdk
--ide IDE The IDE files to generate using GN. Use `gn gen help`
and look for the --ide flag to see supported IDEs. If
this flag is not specified, a platform specific
default is selected.
--disable-desktop-embeddings
Do not include desktop embeddings in the build.
--build-glfw-shell Build the GLFW shell on supported platforms where it
is not built by default.
--no-build-glfw-shell
Do not build the GLFW shell on platforms where it is
built by default.
--bitcode Enable bitcode for iOS targets. On debug runtime
modes, this will be a marker only.
--stripped Strip debug symbols from the output. This defaults to
true and has no effect on iOS.
--no-stripped
--asan
--lsan
--msan
--tsan
--ubsan
6、最后编译出的引擎产物如下
7、用编译出的引擎打包APP
flutter build apk --target-platform android-arm64 --flavor ************ --release --local-engine-src-path /Users/johnson/Desktop/WorkSpace/engine/src --local-engine=android_release_arm64
可能的坑： 在编译2.0.3引擎的时候可能在运行gclient的时候报stagehand错误，原因是这个三方库的地址改变了，在.gclient文件中加上 'src/third_party/dart/third_party/pkg/stagehand':"git@github.com:BuildAndRelease/stagehand.git@e64ac90cac508981011299c4ceb819149e71f1bd"
