Allow GN toolchains to specify runtime deps outputs.

build/toolchain/win/BUILD.gn

Index: build/toolchain/win/BUILD.gn
diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index 7d98b030d515368cf8f5238a9d60ef7c3b62fbc1..d4c6dd46a0cfd5314cbf4b7b6bb6effb200fd855 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -192,6 +192,12 @@ template("msvc_toolchain") {
       ]
       link_output = libname
       depend_output = libname
+
+      # The new version of GN uses a runtime_outputs list rather than a
+      # runtime_link_output string. This needs to be flipped for the next GN
+      # roll.
+      # TODO(brettw) bug 631242: Swap this and remove the old one.
+      #runtime_outputs = [ dllname ]
       runtime_link_output = dllname
 
       # Since the above commands only updates the .lib file when it changes, ask