[unibrow] -1 used by kNoPreviousCharacter and kEndOfInput isn't a valid...

[unibrow] -1 used by kNoPreviousCharacter and kEndOfInput isn't a valid Lead/Trail char. Drop superfluous check.

Change-Id: Ie6b8e61230e25ab0321d0672d71f64fd593714bf
Reviewed-on: https://chromium-review.googlesource.com/1109829
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53924}

src/parsing/scanner.h

@@ -618,8 +618,10 @@ class Scanner {
   }
 
   void HandleLeadSurrogate() {
+    DCHECK(!unibrow::Utf16::IsLeadSurrogate(kEndOfInput));
     if (unibrow::Utf16::IsLeadSurrogate(c0_)) {
       uc32 c1 = source_->Advance();
+      DCHECK(!unibrow::Utf16::IsTrailSurrogate(kEndOfInput));
       if (!unibrow::Utf16::IsTrailSurrogate(c1)) {
         source_->Back();
       } else {

src/unicode-inl.h

@@ -85,6 +85,7 @@ unsigned Utf8::Encode(char* str,
     str[1] = 0x80 | (c & kMask);
     return 2;
   } else if (c <= kMaxThreeByteChar) {
+    DCHECK(!Utf16::IsLeadSurrogate(Utf16::kNoPreviousCharacter));
     if (Utf16::IsSurrogatePair(previous, c)) {
       const int kUnmatchedSize = kSizeOfUnmatchedSurrogate;
       return Encode(str - kUnmatchedSize,
@@ -127,8 +128,8 @@ unsigned Utf8::Length(uchar c, int previous) {
   } else if (c <= kMaxTwoByteChar) {
     return 2;
   } else if (c <= kMaxThreeByteChar) {
-    if (Utf16::IsTrailSurrogate(c) &&
-        Utf16::IsLeadSurrogate(previous)) {
+    DCHECK(!Utf16::IsLeadSurrogate(Utf16::kNoPreviousCharacter));
+    if (Utf16::IsSurrogatePair(previous, c)) {
       return kSizeOfUnmatchedSurrogate - kBytesSavedByCombiningSurrogates;
     }
     return 3;

src/unicode.h

@@ -94,22 +94,20 @@ class UnicodeData {
 
 class Utf16 {
  public:
+  static const int kNoPreviousCharacter = -1;
   static inline bool IsSurrogatePair(int lead, int trail) {
     return IsLeadSurrogate(lead) && IsTrailSurrogate(trail);
   }
   static inline bool IsLeadSurrogate(int code) {
-    if (code == kNoPreviousCharacter) return false;
     return (code & 0xfc00) == 0xd800;
   }
   static inline bool IsTrailSurrogate(int code) {
-    if (code == kNoPreviousCharacter) return false;
     return (code & 0xfc00) == 0xdc00;
   }
 
   static inline int CombineSurrogatePair(uchar lead, uchar trail) {
     return 0x10000 + ((lead & 0x3ff) << 10) + (trail & 0x3ff);
   }
-  static const int kNoPreviousCharacter = -1;
   static const uchar kMaxNonSurrogateCharCode = 0xffff;
   // Encoding a single UTF-16 code unit will produce 1, 2 or 3 bytes
   // of UTF-8 data.  The special case where the unit is a surrogate