Fixes to be able to build Dawn inside Skia

Add a dawn_has_build override similarly to angle_has_build that makes
Dawn not depend on Chromium //build if it can avoid it. (this was
previously used for mac_sdk.gni).

Only load the Vulkan Validation Layers' gni if it is enable via
dawn_enable_vulkan_validation_layers.

Fix a GN build warning where the source of dawn_components would be
built twice: for example libdawn_native.MetalBackend.o would be built
once for libdawn_native static and once for libdawn_native shared. Fix
this by making libdawn_native as a static library libdawn_native_static.

Change-Id: Ib8fb72282435eb475d7a11dae0d5a9977572fd57
Bug: chromium:1064305
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/18963
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

build_overrides/dawn.gni

@@ -20,6 +20,9 @@
 # MUST be unset in other projects (will default to false).
 dawn_standalone = true
 
+# True if Dawn can access build/, testing/ and other Chrome folders.
+dawn_has_build = true
+
 # Defaults for these are set again in dawn_overrides_with_defaults.gni so that
 # users of Dawn don't have to set dirs if they happen to use the same as Dawn.
 

scripts/dawn_component.gni

@@ -107,7 +107,7 @@ template("dawn_component") {
   }
 
   static_library("${libname}_static") {
-    output_name = libname
+    output_name = libname + "_static"
 
     complete_static_lib = dawn_complete_static_libs
 

scripts/dawn_overrides_with_defaults.gni

@@ -24,6 +24,10 @@ if (!defined(dawn_standalone)) {
   dawn_standalone = false
 }
 
+if (!defined(dawn_has_build)) {
+  dawn_has_build = true
+}
+
 if (!defined(dawn_root)) {
   dawn_root = get_path_info("..", "abspath")
 }

src/dawn_native/BUILD.gn

@@ -15,14 +15,21 @@
 import("../../scripts/dawn_overrides_with_defaults.gni")
 
 import("//build_overrides/build.gni")
-import("//build_overrides/vulkan_validation_layers.gni")
 import("${dawn_root}/generator/dawn_generator.gni")
 import("${dawn_root}/scripts/dawn_component.gni")
 import("${dawn_root}/scripts/dawn_features.gni")
 
 # Import mac_min_system_version
 if (is_mac) {
+  if (dawn_has_build) {
     import("//build/config/mac/mac_sdk.gni")
+  } else {
+    mac_min_system_version = "10.11.0"
+  }
+}
+
+if (dawn_enable_vulkan_validation_layers) {
+  import("//build_overrides/vulkan_validation_layers.gni")
 }
 
 # Swiftshader is an optional dependency of Dawn so we only use it if the path