Allow most third_party targets to use system libraries if asked.

This extends the pattern in freetype2 to expat, icu, libjpeg-turbo, libpng, libwebp, and zlib, and gives all these an arg to control which to use.

Homebrew doesn't have dng_sdk, piex, or sftnly, or I'd have done the same for them too.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4260

DOCS_PREVIEW= https://skia.org/?cl=4260

Change-Id: I82e780502bf2217336e791787f172a6fc8f55460
Reviewed-on: https://skia-review.googlesource.com/4260
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Hal Canary <halcanary@google.com>

1 files changed, 34 insertions, 27 deletions

diff --git a/third_party/libpng/BUILD.gn b/third_party/libpng/BUILD.gn
index 5cd865529e..2e3c01c399 100644
--- a/third_party/libpng/BUILD.gn
+++ b/third_party/libpng/BUILD.gn
@@ -4,38 +4,45 @@
 # found in the LICENSE file.
 
 declare_args() {
+  skia_use_system_libpng = false
 }
 
 import("../third_party.gni")
 
-third_party("libpng") {
-  public_include_dirs = [ "." ]
-
-  deps = [
-    "//third_party/zlib",
-  ]
-  sources = [
-    "png.c",
-    "pngerror.c",
-    "pngget.c",
-    "pngmem.c",
-    "pngpread.c",
-    "pngread.c",
-    "pngrio.c",
-    "pngrtran.c",
-    "pngrutil.c",
-    "pngset.c",
-    "pngtrans.c",
-    "pngwio.c",
-    "pngwrite.c",
-    "pngwtran.c",
-    "pngwutil.c",
-  ]
+if (skia_use_system_libpng) {
+  system("libpng") {
+    libs = [ "png" ]
+  }
+} else {
+  third_party("libpng") {
+    public_include_dirs = [ "." ]
 
-  if (current_cpu == "arm" || current_cpu == "arm64") {
-    sources += [
-      "arm/arm_init.c",
-      "arm/filter_neon_intrinsics.c",
+    deps = [
+      "//third_party/zlib",
     ]
+    sources = [
+      "png.c",
+      "pngerror.c",
+      "pngget.c",
+      "pngmem.c",
+      "pngpread.c",
+      "pngread.c",
+      "pngrio.c",
+      "pngrtran.c",
+      "pngrutil.c",
+      "pngset.c",
+      "pngtrans.c",
+      "pngwio.c",
+      "pngwrite.c",
+      "pngwtran.c",
+      "pngwutil.c",
+    ]
+
+    if (current_cpu == "arm" || current_cpu == "arm64") {
+      sources += [
+        "arm/arm_init.c",
+        "arm/filter_neon_intrinsics.c",
+      ]
+    }
   }
 }