Do not use U+0000 as the invalid code point.

third_party/WebKit/Source/core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.cpp

Index: third_party/WebKit/Source/core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.cpp
diff --git a/third_party/WebKit/Source/core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.cpp b/third_party/WebKit/Source/core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.cpp
index 1caa4b8bb58a72aa49236cf7420a714963388d37..88c08051d656cc3e9dfa2bed77db0cc3c567e690 100644
--- a/third_party/WebKit/Source/core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.cpp
+++ b/third_party/WebKit/Source/core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.cpp
@@ -11,6 +11,9 @@
 #include <ostream> // NOLINT
 
 namespace blink {
+namespace {
+const UChar32 kInvalidCodePoint = WTF::Unicode::kMaxCodepoint + 1;
+} // namespace
 
 #define FOR_EACH_FORWARD_GRAPHEME_BOUNDARY_STATE(V)                      \
     /* Counting preceding regional indicators. This is initial state. */ \
@@ -49,14 +52,15 @@ std::ostream& operator<<(std::ostream& os,
 }
 
 ForwardGraphemeBoundaryStateMachine::ForwardGraphemeBoundaryStateMachine()
-    : m_internalState(InternalState::CountRIS)
+    : m_prevCodePoint(kInvalidCodePoint),
+    m_internalState(InternalState::CountRIS)
 {
 }
 
 TextSegmentationMachineState
 ForwardGraphemeBoundaryStateMachine::feedPrecedingCodeUnit(UChar codeUnit)
 {
-    DCHECK_EQ(m_prevCodePoint, 0);
+    DCHECK_EQ(m_prevCodePoint, kInvalidCodePoint);
     DCHECK_EQ(m_boundaryOffset, 0);
     switch (m_internalState) {
     case InternalState::CountRIS:
@@ -106,7 +110,7 @@ ForwardGraphemeBoundaryStateMachine::feedFollowingCodeUnit(UChar codeUnit)
             << " is returned. InternalState: " << m_internalState;
         return finish();
     case InternalState::StartForward:
-        DCHECK_EQ(m_prevCodePoint, 0);
+        DCHECK_EQ(m_prevCodePoint, kInvalidCodePoint);
         DCHECK_EQ(m_boundaryOffset, 0);
         DCHECK_EQ(m_pendingCodeUnit, 0);
         if (U16_IS_TRAIL(codeUnit)) {
@@ -123,7 +127,7 @@ ForwardGraphemeBoundaryStateMachine::feedFollowingCodeUnit(UChar codeUnit)
         m_boundaryOffset = 1;
         return moveToNextState(InternalState::Search);
     case InternalState::StartForwardWaitTrailSurrgate:
-        DCHECK_EQ(m_prevCodePoint, 0);
+        DCHECK_EQ(m_prevCodePoint, kInvalidCodePoint);
         DCHECK_EQ(m_boundaryOffset, 0);
         DCHECK_NE(m_pendingCodeUnit, 0);
         if (U16_IS_TRAIL(codeUnit)) {
@@ -137,7 +141,7 @@ ForwardGraphemeBoundaryStateMachine::feedFollowingCodeUnit(UChar codeUnit)
         m_boundaryOffset = 1;
         return finish();
     case InternalState::Search:
-        DCHECK_NE(m_prevCodePoint, 0);
+        DCHECK_NE(m_prevCodePoint, kInvalidCodePoint);
         DCHECK_NE(m_boundaryOffset, 0);
         DCHECK_EQ(m_pendingCodeUnit, 0);
         if (U16_IS_LEAD(codeUnit)) {
@@ -152,7 +156,7 @@ ForwardGraphemeBoundaryStateMachine::feedFollowingCodeUnit(UChar codeUnit)
         m_boundaryOffset += 1;
         return staySameState();
     case InternalState::SearchWaitTrailSurrogate:
-        DCHECK_NE(m_prevCodePoint, 0);
+        DCHECK_NE(m_prevCodePoint, kInvalidCodePoint);
         DCHECK_NE(m_boundaryOffset, 0);
         DCHECK_NE(m_pendingCodeUnit, 0);
         if (!U16_IS_TRAIL(codeUnit))
@@ -214,7 +218,7 @@ void ForwardGraphemeBoundaryStateMachine::reset()
     m_pendingCodeUnit = 0;
     m_boundaryOffset = 0;
     m_precedingRISCount = 0;
-    m_prevCodePoint = 0;
+    m_prevCodePoint = kInvalidCodePoint;
     m_internalState = InternalState::CountRIS;
 }