Update GN files w/ changes needed to make sanitizers work.

build/config/BUILD.gn

Index: build/config/BUILD.gn
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 8f8a999197d7c844a0f6eb76c17e08294853a776..c06f6ab1852a9a503cb486dc61dc7b48192e4a5f 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -400,6 +400,12 @@ config("executable_config") {
       configs += [ "//build/config/chromecast:executable_config" ]
     }
   }
+
+  # If we're using the prebuilt instrumented libraries with the sanitizers, we
+  # need to add ldflags to every binary to make sure they are picked up.
+  if (prebuilt_instrumented_libraries_available) {
+    configs += [ "//third_party/instrumented_libraries:prebuilt_ldflags" ]
+  }
 }
 
 # Shared library configs -------------------------------------------------------
@@ -415,6 +421,12 @@ config("shared_library_config") {
   } else if (is_chromecast) {
     configs += [ "//build/config/chromecast:shared_library_config" ]
   }
+
+  # If we're using the prebuilt instrumented libraries with the sanitizers, we
+  # need to add ldflags to every binary to make sure they are picked up.
+  if (prebuilt_instrumented_libraries_available) {
+    configs += [ "//third_party/instrumented_libraries:prebuilt_ldflags" ]
+  }
 }
 
 # Add this config to your target to enable precompiled headers.