SharedImageBackingGLImage: Use Retain/Release to scope GL texture

Change SharedImageBackingGLImage to not allocate a GL texture until
it is going to be used, and also delete the GL texture when it is
no longer in use. This is needed for Metal-only SkiaRenderer, where
we really don't want to be using GL (and actually can't, because
there isn't a context hanging around at all times).

TBR=geofflang

Bug: 1092155
Change-Id: I6c14d03b50f40bd96de1c0c7355c03493c22865d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298723Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789707}

gpu/command_buffer/service/shared_image_backing_factory_gl_texture_internal.h

@@ -17,6 +17,7 @@ class SharedImageRepresentationGLTextureClient {
  public:
   virtual bool SharedImageRepresentationGLTextureBeginAccess() = 0;
   virtual void SharedImageRepresentationGLTextureEndAccess() = 0;
+  virtual void SharedImageRepresentationGLTextureRelease(bool have_context) = 0;
 };
 
 // Representation of a SharedImageBackingGLTexture or SharedImageBackingGLImage
@@ -30,6 +31,7 @@ class SharedImageRepresentationGLTextureImpl
       SharedImageRepresentationGLTextureClient* client,
       MemoryTypeTracker* tracker,
       gles2::Texture* texture);
+  ~SharedImageRepresentationGLTextureImpl() override;
 
  private:
   // SharedImageRepresentationGLTexture:
@@ -283,6 +285,7 @@ class SharedImageBackingGLImage
   // SharedImageRepresentationGLTextureClient:
   bool SharedImageRepresentationGLTextureBeginAccess() override;
   void SharedImageRepresentationGLTextureEndAccess() override;
+  void SharedImageRepresentationGLTextureRelease(bool have_context) override;
 
   bool IsPassthrough() const { return is_passthrough_; }
 
@@ -293,11 +296,20 @@ class SharedImageBackingGLImage
   bool BindOrCopyImageIfNeeded();
   bool image_bind_or_copy_needed_ = true;
 
+  void RetainGLTexture();
+  void ReleaseGLTexture(bool have_context);
+  size_t gl_texture_retain_count_ = 0;
+  bool gl_texture_retained_for_legacy_mailbox_ = false;
+
   const SharedImageBackingGLCommon::InitializeGLTextureParams gl_params_;
   const SharedImageBackingFactoryGLTexture::UnpackStateAttribs
       gl_unpack_attribs_;
   const bool is_passthrough_;
 
+  // This is the cleared rect used by ClearedRect and SetClearedRect when
+  // |texture_| is nullptr.
+  gfx::Rect cleared_rect_;
+
   gles2::Texture* rgb_emulation_texture_ = nullptr;
   gles2::Texture* texture_ = nullptr;
   scoped_refptr<gles2::TexturePassthrough> passthrough_texture_;