Fix windows build.

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index d55cde91f879321cae8662585471a19398755664..bee517364a2fc879dbc3f661a33546140323219d 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -1251,10 +1251,10 @@ int OS::StackWalk(Vector<OS::StackFrame> frames) {
     DWORD64 symbol_displacement;
     SmartPointer<IMAGEHLP_SYMBOL64> symbol(
         NewArray<IMAGEHLP_SYMBOL64>(kStackWalkMaxNameLen));
-    if (!symbol) return kStackWalkError;  // Out of memory.
+    if (symbol.is_empty()) return kStackWalkError;  // Out of memory.
     memset(*symbol, 0, sizeof(IMAGEHLP_SYMBOL64) + kStackWalkMaxNameLen);
-    symbol->SizeOfStruct = sizeof(IMAGEHLP_SYMBOL64);
-    symbol->MaxNameLength = kStackWalkMaxNameLen;
+    (*symbol)->SizeOfStruct = sizeof(IMAGEHLP_SYMBOL64);
+    (*symbol)->MaxNameLength = kStackWalkMaxNameLen;
     ok = _SymGetSymFromAddr64(process_handle,             // hProcess
                               stack_frame.AddrPC.Offset,  // Address
                               &symbol_displacement,       // Displacement
@@ -1276,13 +1276,13 @@ int OS::StackWalk(Vector<OS::StackFrame> frames) {
         SNPrintF(MutableCStrVector(frames[frames_count].text,
                                    kStackWalkMaxTextLen),
                  "%s %s:%d:%d",
-                 symbol->Name, Line.FileName, Line.LineNumber,
+                 (*symbol)->Name, Line.FileName, Line.LineNumber,
                  line_displacement);
       } else {
         SNPrintF(MutableCStrVector(frames[frames_count].text,
                                    kStackWalkMaxTextLen),
                  "%s",
-                 symbol->Name);
+                 (*symbol)->Name);
       }
       // Make sure line termination is in place.
       frames[frames_count].text[kStackWalkMaxTextLen - 1] = '\0';