Adding client side field trial for sampling on non-stable channels.

chrome/browser/metrics/chrome_metrics_services_manager_client.h

Index: chrome/browser/metrics/chrome_metrics_services_manager_client.h
diff --git a/chrome/browser/metrics/chrome_metrics_services_manager_client.h b/chrome/browser/metrics/chrome_metrics_services_manager_client.h
index c3fd6c659177213ec12d463fdf75eb1993acab21..0a4ffb17dd10fa9f9592f8d772532ee0c30ddd5e 100644
--- a/chrome/browser/metrics/chrome_metrics_services_manager_client.h
+++ b/chrome/browser/metrics/chrome_metrics_services_manager_client.h
@@ -20,6 +20,10 @@ class EnabledStateProvider;
 class MetricsStateManager;
 }
 
+namespace version_info {
+enum class Channel;
+}
+
 // Provides a //chrome-specific implementation of MetricsServicesManagerClient.
 class ChromeMetricsServicesManagerClient
     : public metrics_services_manager::MetricsServicesManagerClient {
@@ -32,8 +36,10 @@ class ChromeMetricsServicesManagerClient
   // provided. This is expected to occur on first-run on platforms that don't
   // have first-run variations support. This should only be called when there is
   // no existing field trial controlling the sampling feature, and on the
-  // correct platform and channel.
-  static void CreateFallbackSamplingTrial(base::FeatureList* feature_list);
+  // correct platform. |channel| will affect the sampling rates that are
+  // applied. Stable will be sampled at 10%, other channels at 99%.
+  static void CreateFallbackSamplingTrial(version_info::Channel channel,
+                                          base::FeatureList* feature_list);
 
   // Determines if this client is eligible to send metrics. If they are, and
   // there was user consent, then metrics and crashes would be reported.