Canvas 2d: ignore RuntimeEnabledFeatures for LowLatency() cases

ToT looks at RuntimeEnabledFeatures::Canvas2dImageChromiumEnabled()
(enabled by default for Mac, disabled by default elsewhere) to use
ImageCHROMIUM for Canvas 2D contexts or not.  This is fine, but in
the LowLatency it doesn't make sense not use that features, we
always want to use ImageCHROMIUM (if we |want_acceleration| at all).

Hence this CL:
- ignores the RuntimeEnabledFeature if LowLatency (so all platforms
 will use ImageCHROMIUM for LowLatency -- if |want_acceleration|).
- removes the associated code in runtime_features.cc and about_flags.cc,
 essentially undoing my previous crrev.com/c/1056168. (So that Mac
 can still control the use of ImageCHROMIUM for non-low-latency cases).

Bonus cleanup: simplify |enable_web_gl_image_chromium| initialization.

Bug: 878405
Change-Id: I91c5422fad82b1146af02c193546f924bbe5448b
Reviewed-on: https://chromium-review.googlesource.com/1194473
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587930}

chrome/browser/about_flags.cc

@@ -1333,7 +1333,7 @@ const FeatureEntry kFeatureEntries[] = {
      SINGLE_VALUE_TYPE(switches::kIgnoreGpuBlacklist)},
     {"enable-canvas-2d-image-chromium",
      flag_descriptions::kCanvas2DImageChromiumName,
-     flag_descriptions::kCanvas2DImageChromiumDescription, kOsMac | kOsCrOS,
+     flag_descriptions::kCanvas2DImageChromiumDescription, kOsMac,
      FEATURE_VALUE_TYPE(features::kCanvas2DImageChromium)},
     {"disable-accelerated-2d-canvas",
      flag_descriptions::kAccelerated2dCanvasName,

content/child/runtime_features.cc

@@ -174,11 +174,6 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
       !command_line.HasSwitch(switches::kDisable2dCanvasImageChromium) &&
       !command_line.HasSwitch(switches::kDisableGpu) &&
       base::FeatureList::IsEnabled(features::kCanvas2DImageChromium);
-#elif defined(OS_CHROMEOS)
-  const bool enable_canvas_2d_image_chromium =
-      !command_line.HasSwitch(switches::kDisable2dCanvasImageChromium) &&
-      !command_line.HasSwitch(switches::kDisableGpu) &&
-      base::FeatureList::IsEnabled(features::kCanvas2DImageChromium);
 #else
   constexpr bool enable_canvas_2d_image_chromium = false;
 #endif
@@ -186,17 +181,14 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
       enable_canvas_2d_image_chromium);
 
 #if defined(OS_MACOSX)
-  bool enable_web_gl_image_chromium = command_line.HasSwitch(
-      switches::kEnableGpuMemoryBufferCompositorResources) &&
+  const bool enable_web_gl_image_chromium =
+      command_line.HasSwitch(
+          switches::kEnableGpuMemoryBufferCompositorResources) &&
       !command_line.HasSwitch(switches::kDisableWebGLImageChromium) &&
-      !command_line.HasSwitch(switches::kDisableGpu);
-
-  if (enable_web_gl_image_chromium) {
-    enable_web_gl_image_chromium =
-        base::FeatureList::IsEnabled(features::kWebGLImageChromium);
-  }
+      !command_line.HasSwitch(switches::kDisableGpu) &&
+      base::FeatureList::IsEnabled(features::kWebGLImageChromium);
 #else
-  bool enable_web_gl_image_chromium =
+  const bool enable_web_gl_image_chromium =
       command_line.HasSwitch(switches::kEnableWebGLImageChromium);
 #endif
   WebRuntimeFeatures::EnableWebGLImageChromium(enable_web_gl_image_chromium);

third_party/blink/renderer/core/html/canvas/canvas_rendering_context_host.cc

@@ -102,7 +102,8 @@ CanvasRenderingContextHost::GetOrCreateCanvasResourceProviderImpl(
                 : CanvasResourceProvider::kSoftwareCompositedResourceUsage;
 
         const CanvasResourceProvider::PresentationMode presentation_mode =
-            RuntimeEnabledFeatures::Canvas2dImageChromiumEnabled()
+            (RuntimeEnabledFeatures::Canvas2dImageChromiumEnabled() ||
+             (LowLatencyEnabled() && want_acceleration))
                 ? CanvasResourceProvider::kAllowImageChromiumPresentationMode
                 : CanvasResourceProvider::kDefaultPresentationMode;