Move some work from backend onClear to base class clear

src/gpu/GrImmediateDrawTarget.cpp

Index: src/gpu/GrImmediateDrawTarget.cpp
diff --git a/src/gpu/GrImmediateDrawTarget.cpp b/src/gpu/GrImmediateDrawTarget.cpp
index 0cdc645fb427410e3e0881330e5dc2b457988316..f69f86aa5054e67f23a7bc7bf6ae6ed5922e93f9 100644
--- a/src/gpu/GrImmediateDrawTarget.cpp
+++ b/src/gpu/GrImmediateDrawTarget.cpp
@@ -49,9 +49,9 @@ void GrImmediateDrawTarget::onDrawBatch(GrBatch* batch,
     pipeline->~GrPipeline();
 }
 
-void GrImmediateDrawTarget::onClear(const SkIRect* rect, GrColor color,
-                                    bool canIgnoreRect, GrRenderTarget* renderTarget) {
-    this->getGpu()->clear(rect, color, canIgnoreRect, renderTarget);
+void GrImmediateDrawTarget::onClear(const SkIRect& rect, GrColor color,
+                                    GrRenderTarget* renderTarget) {
+    this->getGpu()->clear(rect, color, renderTarget);
 }
 
 void GrImmediateDrawTarget::onCopySurface(GrSurface* dst,