Add support for the ExperimentalSwReporterEngine field trial.

chrome/browser/safe_browsing/srt_fetcher_win.h

Index: chrome/browser/safe_browsing/srt_fetcher_win.h
diff --git a/chrome/browser/safe_browsing/srt_fetcher_win.h b/chrome/browser/safe_browsing/srt_fetcher_win.h
index 6339a001345400ee5d80d764069d565d4c82843d..d1a8872065e341e299c68b63a7a290a21a97e675 100644
--- a/chrome/browser/safe_browsing/srt_fetcher_win.h
+++ b/chrome/browser/safe_browsing/srt_fetcher_win.h
@@ -45,6 +45,15 @@ const int kDaysBetweenSwReporterRunsForPendingPrompt = 1;
 struct SwReporterInvocation {
   base::CommandLine command_line;
 
+  // Experimental versions of the reporter will write metrics to registry keys
+  // ending in |suffix|. Those metrics should be copied to UMA histograms also
+  // ending in |suffix|. For the canonical version, |suffix| will be empty.
+  std::string suffix;
+
+  // The experimental sw_reporter never triggers the prompt, just reports
+  // results through UMA.
+  bool is_experimental = false;

[csharp, 2016/08/25 19:47:29]

What about changing this to be should_prompt or something like that? The main
use case of this seems to now just be deciding if we should prompt. 

[Joe Mason, 2016/08/25 22:03:20]

It also checks whether to report results through Rappor. I plan to gate some
more things on this flag in a followup patch, and then I'd just need to rename
it back again.

+
   SwReporterInvocation();
 
   static SwReporterInvocation FromFilePath(const base::FilePath& exe_path);