Let content_unittests almost build with the components build on android

content/common/android/common_jni_registrar.h

Index: content/common/android/common_jni_registrar.h
diff --git a/content/common/android/common_jni_registrar.h b/content/common/android/common_jni_registrar.h
index fe2855d9e79b4902551c530f64b424e8afa1cfdd..3768bea620a92b1f390e6d35fa738240c151e47f 100644
--- a/content/common/android/common_jni_registrar.h
+++ b/content/common/android/common_jni_registrar.h
@@ -7,11 +7,13 @@
 
 #include <jni.h>
 
+#include "content/common/content_export.h"
+
 namespace content {
 namespace android {
 
 // Register all JNI bindings necessary for content browser.
-bool RegisterCommonJni(JNIEnv* env);
+CONTENT_EXPORT bool RegisterCommonJni(JNIEnv* env);
 
 }  // namespace android
 }  // namespace content