Android WebView: add empty jarjar ruleset.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 5516c63fb77467ce06a27fb98cbce8b1f70b2b7c..69aad8869bf865416dfd58b7971a7d5d9073fe08 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1312,6 +1312,11 @@
         # Copy it out one scope.
         'android_webview_build%': '<(android_webview_build)',
       }],  # OS=="android"
+      ['android_webview_build==1', {
+        # When building the WebView in the Android tree, jarjar will remap all
+        # the class names, so the JNI generator needs to know this.
+        'jni_generator_jarjar_file': '../android_webview/build/jarjar-rules.txt',
+      }],
       ['OS=="mac"', {
         # Enable clang on mac by default!
         'clang%': 1,