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

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

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 383 matching lines @@
 }
 
 TEST(StringTest, Lower)
 {
     EXPECT_STREQ("link", String("LINK").lower().ascii().data());
     EXPECT_STREQ("link", String("lInk").lower().ascii().data());
     EXPECT_STREQ("lin\xE1k", String("lIn\xC1k").lower().latin1().data());
     EXPECT_STREQ("link", String::fromUTF8("LIN\xE2\x84\xAA").lower().utf8().data());
 }
 
+TEST(StringTest, fromUTF8Lenient)

[jsbell, 2016/03/08 20:28:15]

Nit: test name capitalized?

(I know this matches the method name, but that'll be changing soon and this is
really testing round-tripping, not just that method)

[horo, 2016/03/09 01:58:40]

Done.

+{
+    UChar buffer[] = {0x0061 /* 'a' */, 0x0062 /* 'b' */, 0x0063 /* 'c' */, 0xd800 /* surrogate value */};
+    String utf16String(buffer, sizeof(buffer) / sizeof(UChar));
+    ASSERT_FALSE(utf16String.isNull());
+
+    std::string utf8String(utf16String.utf8().data());
+    ASSERT_TRUE(String::fromUTF8(utf8String.data()).isNull());
+    String utf16NewString = String::fromUTF8Lenient(utf8String.data(), utf8String.length());

[jsbell, 2016/03/08 20:28:15]

In addition to testing that fromUTF8Lenient lets these through whereas fromUTF8
returns empty string, we might as well go ahead and test that all 64k code units
make it through cleanly.

I'd also like to see test cases for:

* NUL (U+0000)
* non-ASCII 
* unpaired high surrogate (0xDC00)
* word-swapped surrogates (0xDC00 0xD800)
* a correct surrogate pair (e.g. U+1F4A9 - 0xD83D 0xDCA9)
* non-characters (U+FFFF, etc)

(The multi-unit sequences above wouldn't be exercised by just doing all 64k code
units.)

[horo, 2016/03/09 01:58:40]

Done.

+    ASSERT_FALSE(utf16NewString.isNull());
+    ASSERT_EQ(utf16String, utf16NewString);
+}
+
 } // namespace WTF