Initialize the command line in clear_site_data_fuzzer.cc

After https://chromium-review.googlesource.com/771890, the functionality
tested by this fuzzer depends on base::CommandLine. This was not
initialized in the fuzzer, making it crash.

Bug: 786023
Change-Id: I1c599e3231d5236b6ffb59e20373c2243ee0d026
Reviewed-on: https://chromium-review.googlesource.com/776874Reviewed-by: Max Moroz <mmoroz@chromium.org>
Commit-Queue: Martin Šrámek <msramek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517427}

content/test/fuzzer/clear_site_data_fuzzer.cc

@@ -6,10 +6,16 @@
 #include <stdint.h>
 #include <string>
 
+#include "base/command_line.h"
 #include "content/browser/browsing_data/clear_site_data_throttle.h"  // nogncheck
 
 namespace content {
 
+extern "C" int LLVMFuzzerInitialize(int* argc, char*** argv) {
+  base::CommandLine::Init(*argc, *argv);
+  return 0;
+}
+
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   std::string header(reinterpret_cast<const char*>(data), size);