Create copy of context record before passing it to StackWalk64

StackWalk64 may modify EXCEPTION_POINTERS struct that is passed
to it from constructor of StackTrace.
In the case of StackDumpExceptionFilter the struct that is passed
to constructor of StackTrace may be later passed to other (chained)
exception filter(s), so it shouldn't be modified.

BUG=

Review URL: https://codereview.chromium.org/267463003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269296 0039d316-1c4b-4281-b951-d872f2087c98

base/debug/stack_trace.h

@@ -53,7 +53,7 @@ class BASE_EXPORT StackTrace {
   // Creates a stacktrace for an exception.
   // Note: this function will throw an import not found (StackWalk64) exception
   // on system without dbghelp 5.1.
-  StackTrace(_EXCEPTION_POINTERS* exception_pointers);
+  StackTrace(const _EXCEPTION_POINTERS* exception_pointers);
 #endif
 
   // Copying and assignment are allowed with the default functions.

base/debug/stack_trace_win.cc

@@ -211,22 +211,25 @@ StackTrace::StackTrace() {
 #pragma optimize("", on)
 #endif
 
-StackTrace::StackTrace(EXCEPTION_POINTERS* exception_pointers) {
+StackTrace::StackTrace(const EXCEPTION_POINTERS* exception_pointers) {
   // When walking an exception stack, we need to use StackWalk64().
   count_ = 0;
+  // StackWalk64() may modify context record passed to it, so we will
+  // use a copy.
+  CONTEXT context_record = *exception_pointers->ContextRecord;
   // Initialize stack walking.
   STACKFRAME64 stack_frame;
   memset(&stack_frame, 0, sizeof(stack_frame));
 #if defined(_WIN64)
   int machine_type = IMAGE_FILE_MACHINE_AMD64;
-  stack_frame.AddrPC.Offset = exception_pointers->ContextRecord->Rip;
-  stack_frame.AddrFrame.Offset = exception_pointers->ContextRecord->Rbp;
-  stack_frame.AddrStack.Offset = exception_pointers->ContextRecord->Rsp;
+  stack_frame.AddrPC.Offset = context_record.Rip;
+  stack_frame.AddrFrame.Offset = context_record.Rbp;
+  stack_frame.AddrStack.Offset = context_record.Rsp;
 #else
   int machine_type = IMAGE_FILE_MACHINE_I386;
-  stack_frame.AddrPC.Offset = exception_pointers->ContextRecord->Eip;
-  stack_frame.AddrFrame.Offset = exception_pointers->ContextRecord->Ebp;
-  stack_frame.AddrStack.Offset = exception_pointers->ContextRecord->Esp;
+  stack_frame.AddrPC.Offset = context_record.Eip;
+  stack_frame.AddrFrame.Offset = context_record.Ebp;
+  stack_frame.AddrStack.Offset = context_record.Esp;
 #endif
   stack_frame.AddrPC.Mode = AddrModeFlat;
   stack_frame.AddrFrame.Mode = AddrModeFlat;
@@ -235,7 +238,7 @@ StackTrace::StackTrace(EXCEPTION_POINTERS* exception_pointers) {
                      GetCurrentProcess(),
                      GetCurrentThread(),
                      &stack_frame,
-                     exception_pointers->ContextRecord,
+                     &context_record,
                      NULL,
                      &SymFunctionTableAccess64,
                      &SymGetModuleBase64,