Reland: Switch WTF::find on LChar to use memchr.

third_party/WebKit/Source/wtf/text/StringImpl.h

Index: third_party/WebKit/Source/wtf/text/StringImpl.h
diff --git a/third_party/WebKit/Source/wtf/text/StringImpl.h b/third_party/WebKit/Source/wtf/text/StringImpl.h
index 49c950eba9e480fbc88facdc5565a5b7dfd4e510..22897f18998bd09c2e5588c9f36090b7af8920bc 100644
--- a/third_party/WebKit/Source/wtf/text/StringImpl.h
+++ b/third_party/WebKit/Source/wtf/text/StringImpl.h
@@ -31,6 +31,7 @@
 #include "wtf/WTFExport.h"
 #include "wtf/text/Unicode.h"
 #include <limits.h>
+#include <string.h>
 
 #if OS(MACOSX)
 typedef const struct __CFString * CFStringRef;
@@ -526,8 +527,17 @@ inline bool equalIgnoringASCIICase(const StringImpl* a, const char* b) { return
 
 WTF_EXPORT int codePointCompareIgnoringASCIICase(const StringImpl*, const LChar*);
 
-template<typename CharacterType>
-inline size_t find(const CharacterType* characters, unsigned length, CharacterType matchCharacter, unsigned index = 0)
+inline size_t find(const LChar* characters, unsigned length, LChar matchCharacter, unsigned index = 0)
+{
+    // Some clients rely on being able to pass index >= length.

[Nico, 2016/06/10 19:09:14]

should the clients be fixed instead?

[jbroman, 2016/06/10 19:15:13]

In my ideal world (in which nobody passes out-of-range indexes), yes. But I fear
such sites are subtle and hard to find, except when MSAN happens to find them.

The particular one that was reported was in ContentType::parameter, where
start+1 and start+2 are passed without bounds checking. It's fixable there, but
I suspect other sites also rely on it, and there are many to inspect.

I don't think it's worth doing as part of this wild goose chase, since it's not
super harmful (at least, now that I know that such sites exist).

+    if (index >= length)
+        return kNotFound;
+    const LChar* found = static_cast<const LChar*>(
+        memchr(characters + index, matchCharacter, length - index));
+    return found ? found - characters : kNotFound;
+}
+
+inline size_t find(const UChar* characters, unsigned length, UChar matchCharacter, unsigned index = 0)
 {
     while (index < length) {
         if (characters[index] == matchCharacter)
@@ -549,6 +559,12 @@ inline size_t find(const LChar* characters, unsigned length, UChar matchCharacte
     return find(characters, length, static_cast<LChar>(matchCharacter), index);
 }
 
+template <typename CharacterType>
+inline size_t find(const CharacterType* characters, unsigned length, char matchCharacter, unsigned index = 0)
+{
+    return find(characters, length, static_cast<LChar>(matchCharacter), index);
+}
+
 inline size_t find(const LChar* characters, unsigned length, CharacterMatchFunctionPtr matchFunction, unsigned index = 0)
 {
     while (index < length) {