Add --serial mode to dm, runs unit tests serially

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 5dd8a6f63e96a28387e78ebbd445006ec0dabce3..6d1151737bd2b687f09781ade14fa5eb9b3372eb 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -71,6 +71,10 @@ DEFINE_string(uninterestingHashesFile, "",
 DEFINE_int32(shards, 1, "We're splitting source data into this many shards.");
 DEFINE_int32(shard,  0, "Which shard do I run?");
 
+DEFINE_string2(solo, s, nullptr,
+               "Run the specified tests alone, before creating multiple threads.\n"
+               "Test names must match exactly.  Multiple tests may be separated by spaces.");
+
 DEFINE_string(mskps, "", "Directory to read mskps from, or a single mskp file.");
 
 DEFINE_string(svgs, "", "Directory to read SVGs from, or a single SVG file.");
@@ -1206,7 +1210,7 @@ struct Task {
 
 // Unit tests don't fit so well into the Src/Sink model, so we give them special treatment.
 
-static SkTDArray<skiatest::Test> gParallelTests, gSerialTests;
+static SkTDArray<skiatest::Test> gParallelTests, gSerialTests, gSoloTests;
 
 static void gather_tests() {
     if (!FLAGS_src.contains("tests")) {
@@ -1222,6 +1226,10 @@ static void gather_tests() {
         if (SkCommandLineFlags::ShouldSkip(FLAGS_match, test.name)) {
             continue;
         }
+        if (FLAGS_solo.contains(test.name)) {
+            gSoloTests.push(test);
+            continue;
+        }
         if (test.needsGpu && gpu_supported()) {
             (FLAGS_gpu_threading ? gParallelTests : gSerialTests).push(test);
         } else if (!test.needsGpu && FLAGS_cpu) {
@@ -1317,6 +1325,13 @@ int dm_main() {
         return 1;
     }
     gather_tests();
+
+    // First, run memory intensive tests serially.
+    if (gSoloTests.count() > 0) {
+        info("Running %d tests serially...\n", gSoloTests.count());
+        for (auto test : gSoloTests) { run_test(test); }
+    }
+
     gPending = gSrcs.count() * gSinks.count() + gParallelTests.count() + gSerialTests.count();
     info("%d srcs * %d sinks + %d tests == %d tasks",
          gSrcs.count(), gSinks.count(), gParallelTests.count() + gSerialTests.count(), gPending);