CFX_ByteString::Reserve(), ReleaseBuffer() fixes.

Also identical fixes for CFX_WideString.

Reserve() on an empty string would not actually reserve a
buffer.  Currently unused, but there are places where this
would really help.

ReleaseBuffer() would rarely return memory to the system, since
it would short-circuit thinking it could operate in place.  Tune
the algorithm slightly so that we hold on when the savings is
small.

Bounds check release buffer args rather than just asserting.
Add tests for all of these.

Review URL: https://codereview.chromium.org/1916303004

1 files changed, 8 insertions, 3 deletions

diff --git a/core/fxcrt/fx_basic_bstring.cpp b/core/fxcrt/fx_basic_bstring.cpp
index 1622c4bc55..e098d8fe50 100644
--- a/core/fxcrt/fx_basic_bstring.cpp
+++ b/core/fxcrt/fx_basic_bstring.cpp
@@ -276,20 +276,25 @@ void CFX_ByteString::ReleaseBuffer(FX_STRSIZE nNewLength) {
   if (nNewLength == -1)
     nNewLength = FXSYS_strlen(m_pData->m_String);
 
+  nNewLength = std::min(nNewLength, m_pData->m_nAllocLength);
   if (nNewLength == 0) {
     clear();
     return;
   }
 
-  FXSYS_assert(nNewLength <= m_pData->m_nAllocLength);
-  ReallocBeforeWrite(nNewLength);
+  FXSYS_assert(m_pData->m_nRefs == 1);
   m_pData->m_nDataLength = nNewLength;
   m_pData->m_String[nNewLength] = 0;
+  if (m_pData->m_nAllocLength - nNewLength >= 32) {
+    // Over arbitrary threshold, so pay the price to relocate.  Force copy to
+    // always occur by holding a second reference to the string.
+    CFX_ByteString preserve(*this);
+    ReallocBeforeWrite(nNewLength);
+  }
 }
 
 void CFX_ByteString::Reserve(FX_STRSIZE len) {
   GetBuffer(len);
-  ReleaseBuffer(GetLength());
 }
 
 FX_CHAR* CFX_ByteString::GetBuffer(FX_STRSIZE nMinBufLength) {