aw: Enable SkiaRenderer with VizForWebView

There is few dependencies between features:
VizForWebView requires UseSkiaRenderer and UseSkiaForGLReadback.
UseSkiaRenderer requires EnableSharedImageForWebview.

Previously we enforced dependencies in AwMainDelegate which involves
changing of command line arguments and has two problems:
1. Finch experiments are not initialized yet at that moment, so they
   have to enable four features instead of one.
2. Command line overrides finch trials flags.

This CL changes how we check for features to enforce all dependencies.

Bug: 805739
Change-Id: I34f823640f355637ea0b27d1dec1b5afc3e9bec4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067349Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745270}

android_webview/lib/aw_main_delegate.cc

@@ -182,11 +182,7 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
     // so we can't use FeatureList::IsEnabled. This is necessary if someone
     // enabled feature through command line. Finch experiments will need to set
     // all flags in trial config.
-    if (features.IsEnabled(::features::kVizForWebView)) {
-      features.EnableIfNotSet(::features::kEnableSharedImageForWebview);
-      features.EnableIfNotSet(::features::kUseSkiaForGLReadback);
-      features.EnableIfNotSet(::features::kUseSkiaRenderer);
-    } else {
+    if (!features.IsEnabled(::features::kVizForWebView)) {
       // Viz for WebView is required to support embedding CompositorFrameSinks
       // which is needed for UseSurfaceLayerForVideo feature.
       // https://crbug.com/853832

components/viz/common/features.cc

@@ -72,6 +72,10 @@ bool IsVizHitTestingDebugEnabled() {
 }
 
 bool IsUsingSkiaForGLReadback() {
+  // Viz for webview requires Skia Readback.
+  if (IsUsingVizForWebView())
+    return true;
+
   return base::FeatureList::IsEnabled(kUseSkiaForGLReadback);
 }
 
@@ -84,6 +88,10 @@ bool IsUsingSkiaRenderer() {
     return false;
 #endif
 
+  // Viz for webview requires SkiaRenderer.
+  if (IsUsingVizForWebView())
+    return true;
+
   return base::FeatureList::IsEnabled(kUseSkiaRenderer) ||
          base::FeatureList::IsEnabled(kVulkan);
 }
@@ -100,6 +108,10 @@ bool IsDynamicColorGamutEnabled() {
 #endif
 
 bool IsUsingVizForWebView() {
+  // Viz for WebView requires shared images to be enabled.
+  if (!base::FeatureList::IsEnabled(kEnableSharedImageForWebview))
+    return false;
+
   return base::FeatureList::IsEnabled(kVizForWebView);
 }