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

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 9739210bc2e4eb3584a4f08ede0e3506a6130230..2734b7589abe37c5b8a144a92cd7699a3e5185b1 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -518,16 +518,22 @@ static void run_enclave_and_gpu_tests(SkTArray<Task>* tasks) {
 
 // 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();
@@ -539,8 +545,7 @@ int dm_main() {
         SkInstCountPrintLeaksOnExit();
     }
 
-    SkThread keepAlive(keep_alive);  // This thread will just be killed by processes shutdown.
-    keepAlive.start();
+    start_keepalive();
 
     gather_gold();