Reland "Reland "Have a GrBackendFormat be stored on gpu proxies.""

This is a reland of 2f9a5ea639925f38785f4d3a0af237822007cfd6

Original change's description:
> Reland "Have a GrBackendFormat be stored on gpu proxies."
> 
> This reverts commit 919c9e77c3492af766ff5982acda76ee49da3168.
> 
> Reason for revert: Flutter change has landed and fixed memory issue.
> 
> Original change's description:
> > Revert "Have a GrBackendFormat be stored on gpu proxies."
> >
> > This reverts commit 51b1c12bbc2fa3f8d4faa29ad19c6f3cb34837ce.
> >
> > Reason for revert: reverting till flutter gets to 1.1 to fix build issues.
> >
> > Original change's description:
> > > Have a GrBackendFormat be stored on gpu proxies.
> > >
> > > Bug: skia:
> > > Change-Id: Iaf1fb24ab29a61d44e5fa59a5e0867ed02dcda90
> > > Reviewed-on: https://skia-review.googlesource.com/c/168021
> > > Reviewed-by: Brian Osman <brianosman@google.com>
> > > Commit-Queue: Greg Daniel <egdaniel@google.com>
> >
> > TBR=egdaniel@google.com,bsalomon@google.com,brianosman@google.com
> >
> > Change-Id: I574fdc084ef5994596c51fb0d60423b5dc01b885
> > No-Presubmit: true
> > No-Tree-Checks: true
> > No-Try: true
> > Bug: chromium:903701 chromium:903756
> > Reviewed-on: https://skia-review.googlesource.com/c/169835
> > Commit-Queue: Greg Daniel <egdaniel@google.com>
> > Reviewed-by: Greg Daniel <egdaniel@google.com>
> 
> TBR=egdaniel@google.com,bsalomon@google.com,brianosman@google.com
> 
> Change-Id: Ifd9b6b8e194af9fb9258fa626644e76e6ecf090d
> Bug: chromium:903701 chromium:903756
> Reviewed-on: https://skia-review.googlesource.com/c/170104
> Commit-Queue: Greg Daniel <egdaniel@google.com>
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

Bug: chromium:903701 chromium:903756
Change-Id: Id1360067d8e928b0a4e1848dae8bc1e7f1994403
Reviewed-on: https://skia-review.googlesource.com/c/171660
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/mock/GrMockTexture.h b/src/gpu/mock/GrMockTexture.h
index ebf7b73..0565f81 100644
--- a/src/gpu/mock/GrMockTexture.h
+++ b/src/gpu/mock/GrMockTexture.h
@@ -37,6 +37,10 @@
                                 fInfo);
     }
 
+    GrBackendFormat backendFormat() const override {
+        return GrBackendFormat::MakeMock(fInfo.fConfig);
+    }
+
     void textureParamsModified() override {}
     void setRelease(sk_sp<GrReleaseProcHelper> releaseHelper) override {
         fReleaseHelper = std::move(releaseHelper);
@@ -115,6 +119,10 @@
         return {this->width(), this->height(), this->numColorSamples(), numStencilBits, fInfo};
     }
 
+    GrBackendFormat backendFormat() const override {
+        return GrBackendFormat::MakeMock(fInfo.fConfig);
+    }
+
 protected:
     // constructor for subclasses
     GrMockRenderTarget(GrMockGpu* gpu, const GrSurfaceDesc& desc,
@@ -154,6 +162,10 @@
     const GrTexture* asTexture() const override { return this; }
     const GrRenderTarget* asRenderTarget() const override { return this; }
 
+    GrBackendFormat backendFormat() const override {
+        return GrMockTexture::backendFormat();
+    }
+
 private:
     void onAbandon() override {
         GrRenderTarget::onAbandon();