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

third_party/WebKit/Source/wtf/text/UTF8.cpp

Index: third_party/WebKit/Source/wtf/text/UTF8.cpp
diff --git a/third_party/WebKit/Source/wtf/text/UTF8.cpp b/third_party/WebKit/Source/wtf/text/UTF8.cpp
index 0beca10497c8e8411d13883305a172c28b264b45..4550b77f68e9a498b36a85cbae722fe4997afdfc 100644
--- a/third_party/WebKit/Source/wtf/text/UTF8.cpp
+++ b/third_party/WebKit/Source/wtf/text/UTF8.cpp
@@ -185,7 +185,7 @@ ConversionResult convertUTF16ToUTF8(
 // This must be called with the length pre-determined by the first byte.
 // If presented with a length > 4, this returns false.  The Unicode
 // definition of UTF-8 goes up to 4-byte sequences.
-static bool isLegalUTF8(const unsigned char* source, int length)
+static bool isLegalUTF8(const unsigned char* source, int length, bool strict = true)
 {
     unsigned char a;
     const unsigned char* srcptr = source + length;
@@ -210,7 +210,8 @@ static bool isLegalUTF8(const unsigned char* source, int length)
                 return false;
             break;
         case 0xED:
-            if (a > 0x9F)
+            // Surrogate values are mapped to [EDA080-EDAFBF] and [EDB080-EDBFBF] in lenient mode.
+            if (strict && a > 0x9F)
                 return false;
             break;
         case 0xF0:
@@ -283,7 +284,7 @@ ConversionResult convertUTF8ToUTF16(
             break;
         }
         // Do this check whether lenient or strict
-        if (!isLegalUTF8(reinterpret_cast<const unsigned char*>(source), utf8SequenceLength)) {
+        if (!isLegalUTF8(reinterpret_cast<const unsigned char*>(source), utf8SequenceLength, strict)) {
             result = sourceIllegal;
             break;
         }
@@ -304,8 +305,8 @@ ConversionResult convertUTF8ToUTF16(
                     result = sourceIllegal;
                     break;
                 }
-                *target++ = replacementCharacter;
-                orAllData |= replacementCharacter;
+                *target++ = static_cast<UChar>(character);
+                orAllData |= character;
             } else {
                 *target++ = static_cast<UChar>(character); // normal case
                 orAllData |= character;