Create CrashReportDatabase interface, a test, and a Mac implementation.

util/mac/xattr.cc

Index: util/mac/xattr.cc
diff --git a/util/mac/xattr.cc b/util/mac/xattr.cc
index 750a056d4bac995d64690f8fd4fb5d962281b53c..cdd92090d46f92c764362739057d47a01e6e7d04 100644
--- a/util/mac/xattr.cc
+++ b/util/mac/xattr.cc
@@ -14,6 +14,7 @@
 
 #include "util/mac/xattr.h"
 
+#include <errno.h>
 #include <stdint.h>
 #include <sys/xattr.h>
 
@@ -25,6 +26,15 @@
 
 namespace crashpad {
 
+bool HasXattr(const base::FilePath& file, const base::StringPiece& name) {
+  if (getxattr(file.value().c_str(), name.data(), nullptr, 0, 0, 0) < 0) {
+    PLOG_IF(ERROR, errno != ENOATTR)
+        << "getxattr exists " << name << " on file " << file.value();
+    return false;
+  }
+  return true;
+}
+
 bool ReadXattr(const base::FilePath& file,
                const base::StringPiece& name,
                std::string* value) {