Allow exception handler callbacks more flexibility (#81). r=bryner

- Provide an optional filter callback that gets triggered before attempting
   to write a dump, to give client code a chance to refuse handling early
   in the process.
 - Allow exceptions that are unhandled by Airbag (due to filter callback or
   dump callback return value, or failure to write a dump) to be passed to the
   previous handler or to the system.
 - In order to pass exceptions unhandled by the topmost Airbag handler to
   lower handlers, fix up the stacking of ExceptionHandler objects, and give
   each ExceptionHandler object its own thread (like the Mac implementation)
   to avoid deadlock.
 - Provide a dump_path argument to callbacks, as requested by developers and
   already implemented in the Mac handler.
 - Avoid calling c_str in exception handler code (#90).

http://groups.google.com/group/airbag-dev/browse_thread/thread/4771825ced38a84c


git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@79 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/processor/testdata/minidump2.stackwalk.out

@@ -7,19 +7,19 @@ Crash reason:  EXCEPTION_ACCESS_VIOLATION
 Crash address: 0x45
 
 Thread 0 (crashed)
- 0  test_app.exe!CrashFunction() [test_app.cc : 51 + 0x3]
-    eip = 0x0040208e   esp = 0x0012feec   ebp = 0x0012fef0   ebx = 0x7c80abc1
-    esi = 0x00000002   edi = 0x00000a28   eax = 0x00000045   ecx = 0x0012fefc
-    edx = 0x7c90eb94   efl = 0x00010246
- 1  test_app.exe!main [test_app.cc : 56 + 0x4]
-    eip = 0x004020df   esp = 0x0012fef8   ebp = 0x0012ff70
+ 0  test_app.exe!`anonymous namespace'::CrashFunction [test_app.cc : 56 + 0x3]
+    eip = 0x00403f6e   esp = 0x0012fe8c   ebp = 0x0012fe90   ebx = 0x7c80abc1
+    esi = 0x00000002   edi = 0x00000a28   eax = 0x00000045   ecx = 0x0012fe9c
+    edx = 0x0042ac60   efl = 0x00010246
+ 1  test_app.exe!main [test_app.cc : 63 + 0x4]
+    eip = 0x00403ed0   esp = 0x0012fe98   ebp = 0x0012ff70
  2  test_app.exe!__tmainCRTStartup [crt0.c : 318 + 0x11]
-    eip = 0x0040395c   esp = 0x0012ff78   ebp = 0x0012ffc0
+    eip = 0x00405096   esp = 0x0012ff78   ebp = 0x0012ffc0
  3  kernel32.dll!BaseProcessStart + 0x22
     eip = 0x7c816fd7   esp = 0x0012ffc8   ebp = 0x0012fff0
 
 Loaded modules:
-0x00400000 - 0x0042afff  test_app.exe  ???  (main)
+0x00400000 - 0x0042bfff  test_app.exe  ???  (main)
 0x59a60000 - 0x59b00fff  dbghelp.dll  5.1.2600.2180
 0x76390000 - 0x763acfff  imm32.dll  5.1.2600.2180
 0x76bf0000 - 0x76bfafff  psapi.dll  5.1.2600.2180

src/processor/testdata/test_app.cc

@@ -37,22 +37,29 @@
 
 #include "client/windows/handler/exception_handler.h"
 
-void callback(const std::wstring &id, void *context, bool succeeded) {
+namespace {
+
+static bool callback(const wchar_t *dump_path, const wchar_t *id,
+                     void *context, bool succeeded) {
   if (succeeded) {
-    printf("dump guid is %ws\n", id.c_str());
+    printf("dump guid is %ws\n", id);
   } else {
     printf("dump failed\n");
   }
-  exit(1);
+  fflush(stdout);
+
+  return succeeded;
 }
 
-void CrashFunction() {
+static void CrashFunction() {
   int *i = reinterpret_cast<int*>(0x45);
   *i = 5;  // crash!
 }
 
+}  // namespace
+
 int main(int argc, char **argv) {
-  google_airbag::ExceptionHandler eh(L".", callback, NULL, true);
+  google_airbag::ExceptionHandler eh(L".", NULL, callback, NULL, true);
   CrashFunction();
   printf("did not crash?\n");
   return 0;