win: Fix a few sign mismatch warnings in crashpad.

BUG=chromium:567877
R=mark@chromium.org, scottmg@chromium.org

Review URL: https://codereview.chromium.org/1503403003 .

snapshot/win/process_reader_win.cc

@@ -136,7 +136,7 @@ bool FillThreadContextAndSuspendCount(HANDLE thread_handle,
     CaptureContext(&thread->context.native);
   } else {
     DWORD previous_suspend_count = SuspendThread(thread_handle);
-    if (previous_suspend_count == -1) {
+    if (previous_suspend_count == static_cast<DWORD>(-1)) {
       PLOG(ERROR) << "SuspendThread";
       return false;
     }

util/win/exception_handler_server.cc

@@ -347,7 +347,7 @@ std::wstring ExceptionHandlerServer::CreatePipe() {
 void ExceptionHandlerServer::Run(Delegate* delegate) {
   uint64_t shutdown_token = base::RandUint64();
   ScopedKernelHANDLE thread_handles[kPipeInstances];
-  for (int i = 0; i < arraysize(thread_handles); ++i) {
+  for (size_t i = 0; i < arraysize(thread_handles); ++i) {
     HANDLE pipe;
     if (first_pipe_instance_.is_valid()) {
       pipe = first_pipe_instance_.release();
@@ -399,7 +399,7 @@ void ExceptionHandlerServer::Run(Delegate* delegate) {
   }
 
   // Signal to the named pipe instances that they should terminate.
-  for (int i = 0; i < arraysize(thread_handles); ++i) {
+  for (size_t i = 0; i < arraysize(thread_handles); ++i) {
     ClientToServerMessage message;
     memset(&message, 0, sizeof(message));
     message.type = ClientToServerMessage::kShutdown;