GN: Use interface jars in the classpath to speed up compiling (a little)

build/android/BUILD.gn

Index: build/android/BUILD.gn
diff --git a/build/android/BUILD.gn b/build/android/BUILD.gn
index 5e97d1a47b484f3ce7e1c9e0aadc5e5d1d93a56b..ef953a619a254bab56a0ed1b1e8a9adfc546ddcb 100644
--- a/build/android/BUILD.gn
+++ b/build/android/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/android/rules.gni")
+import("//third_party/ijar/ijar.gni")
 
 sun_tools_jar_path = "$root_gen_dir/sun_tools_jar/tools.jar"
 
@@ -26,6 +27,11 @@ java_prebuilt("sun_tools_java") {
   jar_dep = ":find_sun_tools_jar"
 }
 
+generate_interface_jar("android_ijar") {
+  input_jar = android_sdk_jar
+  output_jar = "$root_out_dir/lib.java/android.interface.jar"
+}
+
 action("cpplib_stripped") {
   _strip_bin = "${android_tool_prefix}strip"
   _soname = "libc++_shared.so"