tracing: Add the TimeTicks clock source as trace metadata

content/browser/tracing/tracing_controller_impl.cc

Index: content/browser/tracing/tracing_controller_impl.cc
diff --git a/content/browser/tracing/tracing_controller_impl.cc b/content/browser/tracing/tracing_controller_impl.cc
index 86b0db3d37e6b2cbe91d9bee9c542b43a4ac71af..06ef7c8f04bb84ba2a6b3fb6f268a1004cf51b05 100644
--- a/content/browser/tracing/tracing_controller_impl.cc
+++ b/content/browser/tracing/tracing_controller_impl.cc
@@ -90,6 +90,24 @@ std::string GetNetworkTypeString() {
   return "Unknown";
 }
 
+std::string GetClockString() {
+  switch (base::TimeTicks::GetClock()) {
+    case base::TimeTicks::Clock::LINUX_CLOCK_MONOTONIC:
+      return "LINUX_CLOCK_MONOTONIC";
+    case base::TimeTicks::Clock::IOS_CF_ABSOLUTE_TIME_MINUS_KERN_BOOTTIME:
+      return "IOS_CF_ABSOLUTE_TIME_MINUS_KERN_BOOTTIME";
+    case base::TimeTicks::Clock::MAC_MACH_ABSOLUTE_TIME:
+      return "MAC_MACH_ABSOLUTE_TIME";
+    case base::TimeTicks::Clock::WIN_QPC:
+      return "WIN_QPC";
+    case base::TimeTicks::Clock::WIN_ROLLOVER_PROTECTED_TIME_GET_TIME:
+      return "WIN_ROLLOVER_PROTECTED_TIME_GET_TIME";
+  }
+
+  NOTREACHED();
+  return std::string();
+}
+
 scoped_ptr<base::DictionaryValue> GenerateTracingMetadataDict()  {
   scoped_ptr<base::DictionaryValue> metadata_dict(new base::DictionaryValue());
 
@@ -145,7 +163,7 @@ scoped_ptr<base::DictionaryValue> GenerateTracingMetadataDict()  {
   if (delegate)
     delegate->GenerateMetadataDict(metadata_dict.get());
 
-  // Highres ticks.
+  metadata_dict->SetString("clock-domain", GetClockString());
   metadata_dict->SetBoolean("highres-ticks",
                             base::TimeTicks::IsHighResolution());