Introduce String::fromUTF8Lenient() and use it for cache_name in CacheStorage API.

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 6371178e6544bbbe3507ea4c292c9b30b25408c4..7cb29ed61d356f0e13f8de6dcbec8d04619c4d82 100644
--- a/third_party/WebKit/Source/platform/exported/WebString.cpp
+++ b/third_party/WebKit/Source/platform/exported/WebString.cpp
@@ -89,6 +89,11 @@ WebString WebString::fromUTF8(const char* data)
     return String::fromUTF8(data);
 }
 
+WebString WebString::fromUTF8Lenient(const char* data, size_t length)
+{
+    return String::fromUTF8Lenient(data, length);
+}
+
 std::string WebString::latin1() const
 {
     String string(m_private.get());