Remove support for GL discards

src/gpu/gl/GrGLGpu.cpp

Index: src/gpu/gl/GrGLGpu.cpp
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index b6add43b2398bd110164f66ccf3f2d956a8b068b..5b24d8a3829d9cfc8993817cab5a8b82bcf6b665 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -2176,55 +2176,6 @@ void GrGLGpu::clear(const SkIRect& rect, GrColor color, GrRenderTarget* target)
     GL_CALL(Clear(GR_GL_COLOR_BUFFER_BIT));
 }
 
-void GrGLGpu::discard(GrRenderTarget* renderTarget) {
-    SkASSERT(renderTarget);
-    if (!this->caps()->discardRenderTargetSupport()) {
-        return;
-    }
-
-    GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(renderTarget);
-    if (renderTarget->getUniqueID() != fHWBoundRenderTargetUniqueID) {
-        fHWBoundRenderTargetUniqueID = SK_InvalidUniqueID;
-        fStats.incRenderTargetBinds();
-        GL_CALL(BindFramebuffer(GR_GL_FRAMEBUFFER, glRT->renderFBOID()));
-    }
-    switch (this->glCaps().invalidateFBType()) {
-        case GrGLCaps::kNone_InvalidateFBType:
-            SkFAIL("Should never get here.");
-            break;
-        case GrGLCaps::kInvalidate_InvalidateFBType:
-            if (0 == glRT->renderFBOID()) {
-                //  When rendering to the default framebuffer the legal values for attachments
-                //  are GL_COLOR, GL_DEPTH, GL_STENCIL, ... rather than the various FBO attachment
-                //  types.
-                static const GrGLenum attachments[] = { GR_GL_COLOR };
-                GL_CALL(InvalidateFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
-                        attachments));
-            } else {
-                static const GrGLenum attachments[] = { GR_GL_COLOR_ATTACHMENT0 };
-                GL_CALL(InvalidateFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
-                        attachments));
-            }
-            break;
-        case GrGLCaps::kDiscard_InvalidateFBType: {
-            if (0 == glRT->renderFBOID()) {
-                //  When rendering to the default framebuffer the legal values for attachments
-                //  are GL_COLOR, GL_DEPTH, GL_STENCIL, ... rather than the various FBO attachment
-                //  types. See glDiscardFramebuffer() spec.
-                static const GrGLenum attachments[] = { GR_GL_COLOR };
-                GL_CALL(DiscardFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
-                        attachments));
-            } else {
-                static const GrGLenum attachments[] = { GR_GL_COLOR_ATTACHMENT0 };
-                GL_CALL(DiscardFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
-                        attachments));
-            }
-            break;
-        }
-    }
-    renderTarget->flagAsResolved();
-}
-
 void GrGLGpu::clearStencil(GrRenderTarget* target) {
     if (nullptr == target) {
         return;