Add metrics to count how often site isolation flags get turned on.

Bug: 794336, 793471
Change-Id: I035823fe6cf0f2f063e58707f3b8a4eba6748ee8
Reviewed-on: https://chromium-review.googlesource.com/823246
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523628}

content/browser/browser_main_loop.cc

@@ -916,6 +916,9 @@ int BrowserMainLoop::PreCreateThreads() {
   policy->AddIsolatedOrigins(
       GetContentClient()->browser()->GetOriginsRequiringDedicatedProcess());
 
+  // Record metrics about which site isolation flags have been turned on.
+  SiteIsolationPolicy::RecordSiteIsolationFlagUsage();
+
   return result_code_;
 }
 

content/common/site_isolation_policy.cc

@@ -94,4 +94,20 @@ std::vector<url::Origin> SiteIsolationPolicy::ParseIsolatedOrigins(
   return origins;
 }
 
+// static
+void SiteIsolationPolicy::RecordSiteIsolationFlagUsage() {
+  // For --site-per-process and --isolate-origins, include flags specified on
+  // command-line, in chrome://flags, and via enterprise policy (i.e., include
+  // switches::kSitePerProcess and switches::kIsolateOrigins).  Exclude these
+  // modes being set through field trials (i.e., exclude
+  // features::kSitePerProcess and features::IsolateOrigins).
+  UMA_HISTOGRAM_BOOLEAN("SiteIsolation.Flags.IsolateOrigins",
+                        base::CommandLine::ForCurrentProcess()->HasSwitch(
+                            switches::kIsolateOrigins));
+
+  UMA_HISTOGRAM_BOOLEAN("SiteIsolation.Flags.SitePerProcess",
+                        base::CommandLine::ForCurrentProcess()->HasSwitch(
+                            switches::kSitePerProcess));
+}
+
 }  // namespace content

content/common/site_isolation_policy.h

@@ -49,6 +49,10 @@ class CONTENT_EXPORT SiteIsolationPolicy {
   // ContentBrowserClient::GetOriginsRequiringDedicatedProcess.
   static std::vector<url::Origin> GetIsolatedOrigins();
 
+  // Records metrics about which site isolation command-line flags are present.
+  // This should be called once on browser startup.
+  static void RecordSiteIsolationFlagUsage();
+
  private:
   SiteIsolationPolicy();  // Not instantiable.
 

tools/metrics/histograms/histograms.xml

@@ -81696,6 +81696,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SiteIsolation.Flags.IsolateOrigins" enum="BooleanEnabled">
+  <owner>alexmos@chromium.org</owner>
+  <summary>
+    True if the --isolate-origins mode was enabled from the command line,
+    about:flags, or enterprise policy.  Recorded on browser startup.
+  </summary>
+</histogram>
+
+<histogram name="SiteIsolation.Flags.SitePerProcess" enum="BooleanEnabled">
+  <owner>alexmos@chromium.org</owner>
+  <summary>
+    True if the --site-per-process mode was enabled from the command line,
+    about:flags, or enterprise policy.  Recorded on browser startup.
+  </summary>
+</histogram>
+
 <histogram name="SiteIsolation.IsolateAllSitesProcessCountEstimate">
   <owner>creis@chromium.org</owner>
   <summary>