DM: wire up --leaks / -l again

No public API changes.
TBR=reed@google.com

BUG=skia:

Review URL: https://codereview.chromium.org/893043002

dm/DM.cpp

@@ -8,6 +8,7 @@
 #include "SkCommonFlags.h"
 #include "SkForceLinking.h"
 #include "SkGraphics.h"
+#include "SkInstCnt.h"
 #include "SkMD5.h"
 #include "SkOSFile.h"
 #include "SkTDynamicHash.h"
@@ -490,6 +491,9 @@ int dm_main() {
     SetupCrashHandler();
     SkAutoGraphics ag;
     SkTaskGroup::Enabler enabled(FLAGS_threads);
+    if (FLAGS_leaks) {
+        SkInstCountPrintLeaksOnExit();
+    }
 
     gather_gold();
 

include/core/SkInstCnt.h

@@ -77,4 +77,6 @@
     #define SK_DECLARE_INST_COUNT(T)
 #endif
 
+void SkInstCountPrintLeaksOnExit();
+
 #endif // SkInstCnt_DEFINED

src/core/SkInstCnt.cpp

@@ -9,4 +9,7 @@
 
 #if SK_ENABLE_INST_COUNT && !defined(SKIA_DLL)  // See SkInstCnt.h
     bool gPrintInstCount = false;
+    void SkInstCountPrintLeaksOnExit() { gPrintInstCount = true; }
+#else
+    void SkInstCountPrintLeaksOnExit() {}
 #endif