Update from https://crrev.com/317530

build/jni_generator.gypi

Index: build/jni_generator.gypi
diff --git a/build/jni_generator.gypi b/build/jni_generator.gypi
index 6edc512ecf4db7bd7700ab7399fcc088a5ae3e31..853b5f6e789bf11fc3b9310a6bb7cc2da12a6ad0 100644
--- a/build/jni_generator.gypi
+++ b/build/jni_generator.gypi
@@ -92,6 +92,14 @@
         '<(DEPTH)/build/android/android_exports.gyp:android_exports',
       ],
     }],
+    ['clang==0', {
+      # Clang builds currently fail with --native_exports_optional due to
+      # http://llvm.org/bugs/show_bug.cgi?id=22602 - only enable for gcc.
+      # http://crbug.com/442327
+      'variables': {
+        'native_exports%': '--native_exports_optional',
+      },
+    }],
   ],
 }