Support creation of StackTrace directly from CONTEXT struct

BUG=

Review URL: https://codereview.chromium.org/896533003

Cr-Commit-Position: refs/heads/master@{#314361}

base/debug/stack_trace.h

@@ -17,6 +17,7 @@
 
 #if defined(OS_WIN)
 struct _EXCEPTION_POINTERS;
+struct _CONTEXT;
 #endif
 
 namespace base {
@@ -54,6 +55,7 @@ class BASE_EXPORT StackTrace {
   // Note: this function will throw an import not found (StackWalk64) exception
   // on system without dbghelp 5.1.
   StackTrace(const _EXCEPTION_POINTERS* exception_pointers);
+  StackTrace(const _CONTEXT* context);
 #endif
 
   // Copying and assignment are allowed with the default functions.
@@ -76,6 +78,10 @@ class BASE_EXPORT StackTrace {
   std::string ToString() const;
 
  private:
+#if defined(OS_WIN)
+  void InitTrace(_CONTEXT* context_record);
+#endif
+
   // From http://msdn.microsoft.com/en-us/library/bb204633.aspx,
   // the sum of FramesToSkip and FramesToCapture must be less than 63,
   // so set it to 62. Even if on POSIX it could be a larger value, it usually

base/debug/stack_trace_win.cc

@@ -214,24 +214,35 @@ StackTrace::StackTrace() {
 #endif
 
 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;
+  InitTrace(&context_record);
+}
+
+StackTrace::StackTrace(const CONTEXT* context) {
+  // StackWalk64() may modify context record passed to it, so we will
+  // use a copy.
+  CONTEXT context_record = *context;
+  InitTrace(&context_record);
+}
+
+void StackTrace::InitTrace(CONTEXT* context_record) {
+  // When walking an exception stack, we need to use StackWalk64().
+  count_ = 0;
   // 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 = context_record.Rip;
-  stack_frame.AddrFrame.Offset = context_record.Rbp;
-  stack_frame.AddrStack.Offset = context_record.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 = context_record.Eip;
-  stack_frame.AddrFrame.Offset = context_record.Ebp;
-  stack_frame.AddrStack.Offset = context_record.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;
@@ -240,7 +251,7 @@ StackTrace::StackTrace(const EXCEPTION_POINTERS* exception_pointers) {
                      GetCurrentProcess(),
                      GetCurrentThread(),
                      &stack_frame,
-                     &context_record,
+                     context_record,
                      NULL,
                      &SymFunctionTableAccess64,
                      &SymGetModuleBase64,