Add explicit conversions methods for WebString <-> string16

third_party/WebKit/Source/platform/exported/WebString.cpp

Index: third_party/WebKit/Source/platform/exported/WebString.cpp
diff --git a/third_party/WebKit/Source/platform/exported/WebString.cpp b/third_party/WebKit/Source/platform/exported/WebString.cpp
index 8e1c81c3d8a1f084d2e545c4ef50af47de77a96e..5ff32e9381c8c28c8495f38d2ef4ed4e45382cee 100644
--- a/third_party/WebKit/Source/platform/exported/WebString.cpp
+++ b/third_party/WebKit/Source/platform/exported/WebString.cpp
@@ -81,6 +81,21 @@ WebString WebString::fromUTF8(const char* data) {
   return String::fromUTF8(data);
 }
 
+WebString WebString::fromUTF16(const base::string16& s) {
+  WebString string;
+  string.assign(s.data(), s.length());
+  return string;
+}
+
+WebString WebString::fromUTF16(const base::NullableString16& s) {
+  WebString string;
+  if (s.is_null())
+    string.reset();
+  else
+    string.assign(s.string().data(), s.string().length());
+  return string;
+}
+
 std::string WebString::latin1() const {
   String string(m_private.get());