Revert of fix uninit immediate mode member var in GrDrawingManager

src/gpu/GrDrawingManager.h

Index: src/gpu/GrDrawingManager.h
diff --git a/src/gpu/GrDrawingManager.h b/src/gpu/GrDrawingManager.h
index 449044f85dce1349d23258aa650d1c237d73b681..bc6f7a361aef839d1ed21670c00bf0eeba55faa6 100644
--- a/src/gpu/GrDrawingManager.h
+++ b/src/gpu/GrDrawingManager.h
@@ -71,8 +71,7 @@
         , fPathRendererChain(nullptr)
         , fSoftwarePathRenderer(nullptr)
         , fFlushState(context->getGpu(), context->resourceProvider())
-        , fFlushing(false)
-        , fIsImmediateMode(isImmediateMode) {
+        , fFlushing(false) {
     }
 
     void abandon();