Allow null jstring to C++ string conversions in release.

base/android/jni_string.cc

Index: base/android/jni_string.cc
diff --git a/base/android/jni_string.cc b/base/android/jni_string.cc
index c24ab36ab5ec35795478e5ca659778fc9ed563f7..f28f6498ece95f400f2a34981030e4693dfac22a 100644
--- a/base/android/jni_string.cc
+++ b/base/android/jni_string.cc
@@ -25,6 +25,11 @@ namespace android {
 
 void ConvertJavaStringToUTF8(JNIEnv* env, jstring str, std::string* result) {
   DCHECK(str);
+  if (!str) {
+    LOG(WARNING) << "ConvertJavaStringToUTF8 called with null string.";
+    result->clear();
+    return;
+  }
   const jsize length = env->GetStringLength(str);
   if (!length) {
     result->clear();
@@ -71,6 +76,11 @@ ScopedJavaLocalRef<jstring> ConvertUTF8ToJavaString(
 
 void ConvertJavaStringToUTF16(JNIEnv* env, jstring str, string16* result) {
   DCHECK(str);
+  if (!str) {
+    LOG(WARNING) << "ConvertJavaStringToUTF16 called with null string.";
+    result->clear();
+    return;
+  }
   const jsize length = env->GetStringLength(str);
   if (!length) {
     result->clear();