Bug 1304790 - Add a telemetry probe that measures how long it takes for a content process to start up and communicate back to the parent, r=mconley data-r=francois

MozReview-Commit-ID: 5OaeqZXL6zS

--HG--
extra : rebase_source : 481daa6ef6b05f9c83698ffa39ed7334cd108b8c

dom/ipc/ContentParent.cpp

@@ -1791,6 +1791,7 @@ ContentParent::LaunchSubprocess(ProcessPriority aInitialPriority /* = PROCESS_PR
 ContentParent::ContentParent(ContentParent* aOpener,
                              const nsAString& aRemoteType)
   : nsIContentParent()
+  , mLaunchTS(TimeStamp::Now())
   , mOpener(aOpener)
   , mRemoteType(aRemoteType)
   , mIsForBrowser(!mRemoteType.IsEmpty())
@@ -2505,6 +2506,10 @@ ContentParent::RecvGetXPCOMProcessAttributes(bool* aIsOffline,
                                              OptionalURIParams* aUserContentCSSURL,
                                              nsTArray<LookAndFeelInt>* aLookAndFeelIntCache)
 {
+  Telemetry::Accumulate(Telemetry::CONTENT_PROCESS_LAUNCH_TIME_MS,
+                        static_cast<uint32_t>((TimeStamp::Now() - mLaunchTS)
+                                              .ToMilliseconds()));
+
   nsCOMPtr<nsIIOService> io(do_GetIOService());
   MOZ_ASSERT(io, "No IO service?");
   DebugOnly<nsresult> rv = io->GetOffline(aIsOffline);

dom/ipc/ContentParent.h

@@ -17,6 +17,7 @@
 #include "mozilla/HalTypes.h"
 #include "mozilla/LinkedList.h"
 #include "mozilla/StaticPtr.h"
+#include "mozilla/TimeStamp.h"
 #include "mozilla/UniquePtr.h"
 
 #include "nsDataHashtable.h"
@@ -1096,6 +1097,7 @@ private:
   // details.
 
   GeckoChildProcessHost* mSubprocess;
+  const TimeStamp mLaunchTS; // used to calculate time to start content process
   ContentParent* mOpener;
 
   nsString mRemoteType;

toolkit/components/telemetry/Histograms.json

@@ -186,6 +186,16 @@
     "high": 1000,
     "n_buckets": 50
   },
+  "CONTENT_PROCESS_LAUNCH_TIME_MS" : {
+    "alert_emails": ["bsmedberg@mozilla.com", "mconley@mozilla.com"],
+    "expires_in_version": "57",
+    "bug_numbers": [1304790],
+    "kind": "exponential",
+    "high": 64000,
+    "n_buckets": 100,
+    "releaseChannelCollection": "opt-out",
+    "description": "Content process launch time until the GetXPCOMProcessAttributes message is received, in milliseconds"
+  },
   "CONTENT_RESPONSE_DURATION" : {
     "alert_emails": ["kgupta@mozilla.com"],
     "bug_numbers": [1261373],