Code change to avoid signed/unsigned mismatch warnings

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 e5f9466b21ff364e8786d5e7012b8beef553ad1c..0aa34171c2ac0d1e195e807016b59b2b0a861bea 100644
--- a/core/fxcrt/include/fx_string.h
+++ b/core/fxcrt/include/fx_string.h
@@ -134,7 +134,9 @@ inline bool operator==(const char* lhs, const CFX_ByteStringC& rhs) {
 inline bool operator!=(const char* lhs, const CFX_ByteStringC& rhs) {
   return rhs != lhs;
 }
-#define FXBSTR_ID(c1, c2, c3, c4) ((c1 << 24) | (c2 << 16) | (c3 << 8) | (c4))
+#define FXBSTR_ID(c1, c2, c3, c4)                                      \
+  (((uint32_t)c1 << 24) | ((uint32_t)c2 << 16) | ((uint32_t)c3 << 8) | \
+   ((uint32_t)c4))
 
 // A mutable string with shared buffers using copy-on-write semantics that
 // avoids the cost of std::string's iterator stability guarantees.