Add immediate mode option for gpu configs in dm

Review URL: https://codereview.chromium.org/1421853002
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 9a61b02..cf9a6a2 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -917,8 +917,13 @@
 
 void PreAbandonGpuContextErrorHandler(SkError, void*) {}
 
+DEFINE_bool(imm, false, "Run gpu configs in immediate mode.");
+
 Error GPUSink::draw(const Src& src, SkBitmap* dst, SkWStream*, SkString* log) const {
     GrContextOptions options;
+    if (FLAGS_imm) {
+        options.fImmediateMode = true;
+    }
     src.modifyGrContextOptions(&options);
 
     GrContextFactory factory(options);