Rejigger keep-alive thread so TSAN and LSAN don't complain.

dm/DM.cpp

 #include "CrashHandler.h"
 #include "DMJsonWriter.h"
 #include "DMSrcSink.h"
 #include "DMSrcSinkAndroid.h"
 #include "OverwriteLine.h"
 #include "ProcStats.h"
 #include "SkBBHFactory.h"
 #include "SkChecksum.h"
 #include "SkCommonFlags.h"
 #include "SkForceLinking.h"
@@ skipping 500 matching lines @@
 // If we're isolating all GPU-bound work to one thread (the default), this function runs all that.
 static void run_enclave_and_gpu_tests(SkTArray<Task>* tasks) {
     run_enclave(tasks);
     for (int i = 0; i < gGPUTests.count(); i++) {
         run_test(&gGPUTests[i]);
     }
 }
 
 // Some runs (mostly, Valgrind) are so slow that the bot framework thinks we've hung.
 // This prints something every once in a while so that it knows we're still working.
-static void keep_alive(void*) {
-    for (;;) {
-        static const int kSec = 300;
-#if defined(SK_BUILD_FOR_WIN)
-        Sleep(kSec * 1000);
-#else
-        sleep(kSec);
-#endif
-        SkDebugf("\nStill alive: doing science, reticulating splines...\n");
-    }
+static void start_keepalive() {
+    struct Loop {
+        static void forever(void*) {
+            for (;;) {
+                static const int kSec = 300;
+            #if defined(SK_BUILD_FOR_WIN)
+                Sleep(kSec * 1000);
+            #else
+                sleep(kSec);
+            #endif
+                SkDebugf("\nStill alive: doing science, reticulating splines...\n");
+            }
+        }
+    };
+    static SkThread* intentionallyLeaked = new SkThread(Loop::forever);
+    intentionallyLeaked->start();
 }
 
 int dm_main();
 int dm_main() {
     SetupCrashHandler();
     SkAutoGraphics ag;
     SkTaskGroup::Enabler enabled(FLAGS_threads);
     if (FLAGS_leaks) {
         SkInstCountPrintLeaksOnExit();
     }
 
-    SkThread keepAlive(keep_alive);  // This thread will just be killed by processes shutdown.
-    keepAlive.start();
+    start_keepalive();
 
     gather_gold();
 
     gather_srcs();
     gather_sinks();
     gather_tests();
 
     gPending = gSrcs.count() * gSinks.count() + gThreadedTests.count() + gGPUTests.count();
     SkDebugf("%d srcs * %d sinks + %d tests == %d tasks\n",
              gSrcs.count(), gSinks.count(), gThreadedTests.count() + gGPUTests.count(), gPending);
@@ skipping 42 matching lines @@
     }
     return 0;
 }
 
 #if !defined(SK_BUILD_FOR_IOS) && !defined(SK_BUILD_FOR_NACL)
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return dm_main();
 }
 #endif