Make iterator string types match map container string types

Fixes a compilation error when ::string != std::string.

Bug:
Change-Id: Ifa782da65dd08973de1fc4215f658c798ae5160b
Reviewed-on: https://chromium-review.googlesource.com/802324
Reviewed-by: Mark Mentovai <mark@chromium.org>
diff --git a/src/processor/minidump.cc b/src/processor/minidump.cc
index 81114e0..5defe41 100644
--- a/src/processor/minidump.cc
+++ b/src/processor/minidump.cc
@@ -4904,7 +4904,7 @@
          MDGUIDToString(crashpad_info_.report_id).c_str());
   printf("  client_id = %s\n",
          MDGUIDToString(crashpad_info_.client_id).c_str());
-  for (std::map<string, string>::const_iterator iterator =
+  for (std::map<std::string, std::string>::const_iterator iterator =
            simple_annotations_.begin();
        iterator != simple_annotations_.end();
        ++iterator) {
@@ -4928,7 +4928,7 @@
              module_crashpad_info_list_annotations_
                  [module_index][annotation_index].c_str());
     }
-    for (std::map<string, string>::const_iterator iterator =
+    for (std::map<std::string, std::string>::const_iterator iterator =
              module_crashpad_info_simple_annotations_[module_index].begin();
          iterator !=
              module_crashpad_info_simple_annotations_[module_index].end();