Totally serialize gpu tests on Windows.

dm/DM.cpp

 #include "CrashHandler.h"
 #include "DMJsonWriter.h"
 #include "DMSrcSink.h"
 #include "OverwriteLine.h"
 #include "ProcStats.h"
 #include "SkBBHFactory.h"
 #include "SkCommonFlags.h"
 #include "SkForceLinking.h"
 #include "SkGraphics.h"
 #include "SkMD5.h"
@@ skipping 426 matching lines @@
         }
     }
 
     SK_COMPILE_ASSERT(kAnyThread_Enclave == 0, AnyThreadZero);
     SkTaskGroup tg;
         tg.batch(  Task::Run, enclaves[0].begin(), enclaves[0].count());
         tg.batch(run_enclave,          enclaves+1,      kNumEnclaves-1);
         tg.batch(   run_test,   gCPUTests.begin(),   gCPUTests.count());
         if (FLAGS_gpu_threading) {
             tg.batch(run_test,  gGPUTests.begin(),   gGPUTests.count());
+        #if !defined(SK_BUILD_FOR_WIN32)
         } else {
             for (int i = 0; i < gGPUTests.count(); i++) {
                 run_test(&gGPUTests[i]);
             }
+        #endif
         }
     tg.wait();
+    // At this point we're back in single-threaded land.
 
-    // At this point we're back in single-threaded land.
+    // This is not ideal for parallelism, but Windows seems crash-prone if we run
+    // these GPU tests in parallel with any GPU Src/Sink work.  Everyone else seems fine.
+#if defined(SK_BUILD_FOR_WIN32)
+    for (int i = 0; i < gGPUTests.count(); i++) {
+        run_test(&gGPUTests[i]);
+    }
+#endif
+
     SkDebugf("\n");
-
     JsonWriter::DumpJson();
 
     if (gFailures.count() > 0) {
         SkDebugf("Failures:\n");
         for (int i = 0; i < gFailures.count(); i++) {
             SkDebugf("\t%s", gFailures[i].c_str());
         }
         SkDebugf("%d failures\n", gFailures.count());
         return 1;
     }
     if (gPending > 0) {
         SkDebugf("Hrm, we didn't seem to run everything we intended to!  Please file a bug.\n");
         return 1;
     }
     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