Always use RGBA color type for WebView

For WebView the render target is provided by hwui (except when we use
intermediate FBO to support stenil) and we don't know whether it
supports alpha or not. So we assume always RGBA format

Change-Id: Icbc3464961147a172e767d1ebdc8f7b9944479ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2329918Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793578}

components/viz/service/display_embedder/skia_output_device_webview.cc

@@ -36,17 +36,7 @@ SkiaOutputDeviceWebView::SkiaOutputDeviceWebView(
   DCHECK(context_state_->gr_context());
   DCHECK(context_state_->context());
 
-  // Get alpha bits from the default frame buffer.
-  glBindFramebufferEXT(GL_FRAMEBUFFER,
-                       gl_surface_->GetBackingFramebufferObject());
-  context_state_->gr_context()->resetContext(kRenderTarget_GrGLBackendState);
-  GLint alpha_bits = 0;
-  glGetIntegerv(GL_ALPHA_BITS, &alpha_bits);
-  CHECK_GL_ERROR();
-  supports_alpha_ = alpha_bits > 0;
-
-  capabilities_.sk_color_type =
-      supports_alpha_ ? kRGBA_8888_SkColorType : kRGB_888x_SkColorType;
+  capabilities_.sk_color_type = kRGBA_8888_SkColorType;
   capabilities_.gr_backend_format =
       context_state_->gr_context()->defaultBackendFormat(
           capabilities_.sk_color_type, GrRenderable::kYes);
@@ -109,9 +99,8 @@ void SkiaOutputDeviceWebView::InitSkiaSurface(unsigned int fbo) {
 
   GrGLFramebufferInfo framebuffer_info;
   framebuffer_info.fFBOID = fbo;
-  framebuffer_info.fFormat = supports_alpha_ ? GL_RGBA8 : GL_RGB8_OES;
-  DCHECK_EQ(capabilities_.gr_backend_format.asGLFormat(),
-            supports_alpha_ ? GrGLFormat::kRGBA8 : GrGLFormat::kRGB8);
+  framebuffer_info.fFormat = GL_RGBA8;
+  DCHECK_EQ(capabilities_.gr_backend_format.asGLFormat(), GrGLFormat::kRGBA8);
   SkColorType color_type = capabilities_.sk_color_type;
 
   GrBackendRenderTarget render_target(size_.width(), size_.height(),

components/viz/service/display_embedder/skia_output_device_webview.h

@@ -58,8 +58,6 @@ class SkiaOutputDeviceWebView : public SkiaOutputDevice {
   gfx::ColorSpace color_space_;
   unsigned int last_frame_buffer_object_ = -1;
 
-  bool supports_alpha_ = false;
-
   base::WeakPtrFactory<SkiaOutputDeviceWebView> weak_ptr_factory_{this};
 };