Avoid copying in TrimRight() and TrimLeft() if possible.

core/fxcrt/include/fx_string.h

Index: core/fxcrt/include/fx_string.h
diff --git a/core/fxcrt/include/fx_string.h b/core/fxcrt/include/fx_string.h
index 5e3cb45fba3b0c16fef2f12517b48574a8a1ddb3..38328dabdeffba31e6f350953ce5ba2b92d61612 100644
--- a/core/fxcrt/include/fx_string.h
+++ b/core/fxcrt/include/fx_string.h
@@ -167,14 +167,14 @@ class CFX_ByteString {
   static CFX_ByteString FromUnicode(const CFX_WideString& str);
 
   // Explicit conversion to C-style string.
-  // Note: |this| must outlive the use of the result.
+  // Note: Any subsequent modification of |this| will invalidate the result.
   const FX_CHAR* c_str() const { return m_pData ? m_pData->m_String : ""; }
 
   // Implicit conversion to C-style string -- deprecated.
   operator const FX_CHAR*() const { return m_pData ? m_pData->m_String : ""; }
 
   // Explicit conversion to uint8_t*.
-  // Note: |this| must outlive the use of the result.
+  // Note: Any subsequent modification of |this| will invalidate the result.
   const uint8_t* raw_str() const {
     return m_pData ? reinterpret_cast<const uint8_t*>(m_pData->m_String)
                    : nullptr;
@@ -187,7 +187,7 @@ class CFX_ByteString {
   }
 
   // Explicit conversion to CFX_ByteStringC.
-  // Note: |this| must outlive the use of the result.
+  // Note: Any subsequent modification of |this| will invalidate the result.
   CFX_ByteStringC AsStringC() const {
     return CFX_ByteStringC(raw_str(), GetLength());
   }
@@ -503,15 +503,15 @@ class CFX_WideString {
   static FX_STRSIZE WStringLength(const unsigned short* str);
 
   // Explicit conversion to C-style wide string.
-  // Note: |this| must outlive the use of the result.
+  // Note: Any subsequent modification of |this| will invalidate the result.
   const FX_WCHAR* c_str() const { return m_pData ? m_pData->m_String : L""; }
 
   // Implicit conversion to C-style wide string -- deprecated.
-  // Note: |this| must outlive the use of the result.
+  // Note: Any subsequent modification of |this| will invalidate the result.
   operator const FX_WCHAR*() const { return m_pData ? m_pData->m_String : L""; }
 
   // Explicit conversion to CFX_WideStringC.
-  // Note: |this| must outlive the use of the result.
+  // Note: Any subsequent modification of |this| will invalidate the result.
   CFX_WideStringC AsStringC() const {
     return CFX_WideStringC(c_str(), GetLength());
   }