Add an override flag to enable metrics reporting.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index c8a32d02b4314dd399995f010908eacb99b60fd0..5740b16ba4e1b4ae2621c9d96dca3a7eca6c307c 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -356,6 +356,10 @@ const char kEnableMaterialDesignFeedback[] = "enable-md-feedback";
 // Enables the Material Design policy page at chrome://md-policy.
 const char kEnableMaterialDesignPolicyPage[]  = "enable-md-policy-page";
 
+// Forces metrics reporting to be enabled and may tag logs as examples.

[Alexei Svitkine (slow), 2017/05/04 21:36:01]

Nit: Omit the "and may tag logs as examples" part. It can be re-added if we ever
implement something like that.

[Steven Holte, 2017/05/04 22:07:04]

Done.

+const char kEnableMetricsReportingForTesting[] =
+    "enable-metrics-reporting-for-testing";
+
 // Runs the Native Client inside the renderer process and enables GPU plugin
 // (internally adds lEnableGpuPlugin to the command line).
 const char kEnableNaCl[]                    = "enable-nacl";