Revert "Clear and discard stencil buffers on tilers"

This reverts commit 7b2c85577d79bf1bda6b57d9af8ad793e2fc4862.

Reason for revert: nanobench hangs on chromebook bots during mipmap regeneration

Original change's description:
> Clear and discard stencil buffers on tilers
>
> Bug: skia:
> Change-Id: I42e99cb75567825ac7751fc0ec56e4c45132628b
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/210425
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Chris Dalton <csmartdalton@google.com>

TBR=egdaniel@google.com,robertphillips@google.com,csmartdalton@google.com

Change-Id: I69e04c4797b6bde934d86c83bf0348c8abadcfc3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/213824
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
diff --git a/src/gpu/gl/GrGLGpuCommandBuffer.cpp b/src/gpu/gl/GrGLGpuCommandBuffer.cpp
index 655b915..1412aa3 100644
--- a/src/gpu/gl/GrGLGpuCommandBuffer.cpp
+++ b/src/gpu/gl/GrGLGpuCommandBuffer.cpp
@@ -11,9 +11,22 @@
 #include "src/gpu/GrFixedClip.h"
 #include "src/gpu/GrRenderTargetPriv.h"
 
-void GrGLGpuRTCommandBuffer::set(
-        GrRenderTarget* rt, GrSurfaceOrigin origin, const LoadAndStoreInfo& colorInfo,
-        const StencilLoadAndStoreInfo& stencilInfo) {
+void GrGLGpuRTCommandBuffer::begin() {
+    if (GrLoadOp::kClear == fColorLoadAndStoreInfo.fLoadOp) {
+        fGpu->clear(GrFixedClip::Disabled(), fColorLoadAndStoreInfo.fClearColor,
+                    fRenderTarget, fOrigin);
+    }
+    if (GrLoadOp::kClear == fStencilLoadAndStoreInfo.fLoadOp) {
+        GrStencilAttachment* sb = fRenderTarget->renderTargetPriv().getStencilAttachment();
+        if (sb && (sb->isDirty() || fRenderTarget->alwaysClearStencil())) {
+            fGpu->clearStencil(fRenderTarget, 0x0);
+        }
+    }
+}
+
+void GrGLGpuRTCommandBuffer::set(GrRenderTarget* rt, GrSurfaceOrigin origin,
+                                 const GrGpuRTCommandBuffer::LoadAndStoreInfo& colorInfo,
+                                 const GrGpuRTCommandBuffer::StencilLoadAndStoreInfo& stencilInfo) {
     SkASSERT(fGpu);
     SkASSERT(!fRenderTarget);
     SkASSERT(fGpu == rt->getContext()->priv().getGpu());