Bug 1274041 - Initialize jprof in child process. r=jesup

This makes a function call in XRE_InitChildProcess for the child process that
currently exists in XREMain::XRE_mainStartup for the parent process.

This allows signals that jprof uses to be sent to a child process to
profile that child process.

MozReview-Commit-ID: CeWnYl4LJyA

toolkit/xre/nsEmbedFunctions.cpp

@@ -95,6 +95,10 @@ using mozilla::_ipdltest::IPDLUnitTestProcessChild;
 #include "nsXREAppData.h"
 #endif
 
+#ifdef MOZ_JPROF
+#include "jprof.h"
+#endif
+
 using namespace mozilla;
 
 using mozilla::ipc::BrowserProcessSubThread;
@@ -308,6 +312,11 @@ XRE_InitChildProcess(int aArgc,
   DllBlocklist_Initialize();
 #endif
 
+#ifdef MOZ_JPROF
+  // Call the code to install our handler
+  setupProfilingStuff();
+#endif
+
   // This is needed by Telemetry to initialize histogram collection.
   UniquePtr<base::StatisticsRecorder> statisticsRecorder =
     MakeUnique<base::StatisticsRecorder>();