Add gn Blink GC plugin options

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 74a2d8df016aae707f8ae7aa1802c1aee2d2e95b..dddbf2fa49410578aa913c4d82e38e7c749026d6 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -4,6 +4,7 @@
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
+import("//build/config/clang/clang.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 
@@ -50,10 +51,10 @@ group("deps_no_options") {
     } else {
       exe = ""
     }
-    data += [ "//third_party//llvm-build/Release+Asserts/bin/llvm-symbolizer${exe}" ]
+    data += [ "$clang_base_path/bin/llvm-symbolizer${exe}" ]

[Nico, 2016/06/22 20:01:56]

not sure about the changes in this file -- these don't exist in normal local
builds but are put there by the clang packaging script. But let's go with this
for now.

     if (is_linux) {
       # llvm-symbolizer needs this.
-      data += [ "//third_party/llvm-build/Release+Asserts/lib/libstdc++.so.6" ]
+      data += [ "$clang_base_path/lib/libstdc++.so.6" ]
     }
 
     if (use_prebuilt_instrumented_libraries) {
@@ -76,7 +77,7 @@ group("deps_no_options") {
 if (is_mac && using_sanitizer) {
   copy("copy_asan_runtime") {
     sources = [
-      "//third_party/llvm-build/Release+Asserts/lib/clang/$clang_version/lib/darwin/libclang_rt.asan_osx_dynamic.dylib",
+      "$clang_base_path/lib/clang/$clang_version/lib/darwin/libclang_rt.asan_osx_dynamic.dylib",
     ]
     outputs = [
       "$root_out_dir/{{source_file_part}}",