GN: Android Vulkan support

Android's the easiest place to start supporting Vulkan, so it's up first.

ndk_api becomes user-specifiable so that the Vulkan bots can kick it up
to 24, the first release supporting Vulkan.  The defaults remain the same:
18 for 32-bit and 21 for 64-bit, the first release supporting 64-bit.

To test this, I set ndk_api=24 and skia_use_vulkan=true in GN, then
   $ ninja -C out dm; and droid out/dm --config vk --src gm

Seems to work!  Bot scripts to follow.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2336343002

Review-Url: https://codereview.chromium.org/2336343002

BUILD.gn

@@ -16,6 +16,7 @@ declare_args() {
   skia_use_libpng = true
   skia_use_libwebp = !is_fuchsia
   skia_use_sfntly = !is_fuchsia
+  skia_use_vulkan = false
   skia_use_zlib = true
 }
 
@@ -205,6 +206,7 @@ template("optional") {
                              [
                                "public_defines",
                                "deps",
+                               "libs",
                                "sources",
                                "sources_when_disabled",
                              ])
@@ -339,6 +341,13 @@ optional("typeface_freetype") {
   ]
 }
 
+optional("vulkan") {
+  enabled = skia_use_vulkan
+  public_defines = [ "SK_VULKAN" ]
+  libs = [ "vulkan" ]
+  sources = skia_vk_sources
+}
+
 optional("webp") {
   enabled = skia_use_libwebp
   public_defines = [ "SK_HAS_WEBP_LIBRARY" ]
@@ -390,6 +399,7 @@ component("skia") {
     ":sse42",
     ":ssse3",
     ":typeface_freetype",
+    ":vulkan",
     ":webp",
     ":xml",
   ]
@@ -604,6 +614,10 @@ if (skia_enable_tools) {
     } else if (is_mac) {
       sources += [ "tools/gpu/gl/mac/CreatePlatformGLTestContext_mac.cpp" ]
     }
+
+    if (skia_use_vulkan) {
+      sources += [ "tools/gpu/vk/VkTestContext.cpp" ]
+    }
   }
 
   test_lib("flags") {

gn/BUILDCONFIG.gn

@@ -9,6 +9,7 @@ declare_args() {
   is_debug = true
   is_component_build = false
   ndk = ""
+  ndk_api = 0  # 0 == picked automatically for target_cpu.
   sanitize = ""
 }
 
@@ -45,7 +46,15 @@ if (is_android) {
   ndk_target = ""
   ndk_platform = ""
   ndk_stdlib = ""
-  nkd_gccdir = ""
+  ndk_gccdir = ""
+
+  if (ndk_api == 0) {
+    ndk_api = 18
+    if (target_cpu == "arm64" || target_cpu == "mips64el" ||
+        target_cpu == "x64") {
+      ndk_api = 21
+    }
+  }
 
   if (host_os == "linux") {
     ndk_host = "linux-x86_64"
@@ -55,32 +64,32 @@ if (is_android) {
 
   if (target_cpu == "arm64") {
     ndk_target = "aarch64-linux-android"
-    ndk_platform = "android-21/arch-arm64"
+    ndk_platform = "android-${ndk_api}/arch-arm64"
     ndk_stdlib = "arm64-v8a"
     ndk_gccdir = ndk_target
   } else if (target_cpu == "arm") {
     ndk_target = "arm-linux-androideabi"
-    ndk_platform = "android-18/arch-arm"
+    ndk_platform = "android-${ndk_api}/arch-arm"
     ndk_stdlib = "armeabi-v7a"
     ndk_gccdir = ndk_target
   } else if (target_cpu == "mips64el") {
     ndk_target = "mips64el-linux-android"
-    ndk_platform = "android-21/arch-mips64"
+    ndk_platform = "android-${ndk_api}/arch-mips64"
     ndk_stdlib = "mips64"
     ndk_gccdir = ndk_target
   } else if (target_cpu == "mipsel") {
     ndk_target = "mipsel-linux-android"
-    ndk_platform = "android-18/arch-mips"
+    ndk_platform = "android-${ndk_api}/arch-mips"
     ndk_stdlib = "mips"
     ndk_gccdir = ndk_target
   } else if (target_cpu == "x64") {
     ndk_target = "x86_64-linux-android"
-    ndk_platform = "android-21/arch-x86_64"
+    ndk_platform = "android-${ndk_api}/arch-x86_64"
     ndk_stdlib = "x86_64"
     ndk_gccdir = ndk_stdlib
   } else if (target_cpu == "x86") {
     ndk_target = "i686-linux-android"
-    ndk_platform = "android-18/arch-x86"
+    ndk_platform = "android-${ndk_api}/arch-x86"
     ndk_stdlib = "x86"
     ndk_gccdir = ndk_stdlib
   }

gn/shared_sources.gni

@@ -44,6 +44,7 @@ _gpu_gypi = exec_script("gypi_to_gn.py",
                         [ "../gyp/gpu.gypi" ])
 skia_gpu_sources = _gpu_gypi.skgpu_sources
 skia_null_gpu_sources = _gpu_gypi.skgpu_null_gl_sources
+skia_vk_sources = _gpu_gypi.skgpu_vk_sources
 
 # Opts.
 #