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

third_party/WebKit/public/platform/WebString.h

Index: third_party/WebKit/public/platform/WebString.h
diff --git a/third_party/WebKit/public/platform/WebString.h b/third_party/WebKit/public/platform/WebString.h
index 8e4bbcc473ca4f4d985f70d943cf953a5734dfad..72059488513de70db7f7f50c6f00add9c1a5d25c 100644
--- a/third_party/WebKit/public/platform/WebString.h
+++ b/third_party/WebKit/public/platform/WebString.h
@@ -95,6 +95,13 @@ public:
         return fromUTF8(s.data(), s.length());
     }
 
+    BLINK_COMMON_EXPORT static WebString fromUTF8Lenient(const char* data, size_t length);
+
+    static WebString fromUTF8Lenient(const std::string& s)
+    {
+        return fromUTF8Lenient(s.data(), s.length());
+    }
+
     BLINK_COMMON_EXPORT std::string latin1() const;
 
     BLINK_COMMON_EXPORT static WebString fromLatin1(const WebLChar* data, size_t length);