Enable GPU acceleration in 2D OffscreenCanvases on main thread

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in

 // http://dev.chromium.org/blink/runtime-enabled-features
 //
 // This list is used to generate RuntimeEnabledFeatures.h/cpp which contains
 // a class that stores static enablers for all experimental features.
 //
 // Each feature can be assigned a "status":
 // status=stable -> Enable this in all Blink configurations.  We are committed to these APIs indefinitely.
 // status=experimental -> In-progress features, Web Developers might play with, but are not on by default in stable.
 // status=test -> Enabled in ContentShell for testing, otherwise off.
 // Features without a status are not enabled anywhere by default.
 //
 // "implied_by" or "depends_on" specifies relationship to other features:
 // implied_by=feature1[,feature2,...] -> The feature is automatically enabled if any implied_by features is enabled;
 // depends_on=feature1[,feature2,...] -> The feature is enabled only if all depends_on features are enabled.
 // Only one of "implied_by" and "depends_on" can be specified.
 //
 // "stable" features listed here should be rare, as anything which we've shipped stable
 // can have its runtime flag removed soon after.
 //
 // origin_trial_feature_name=FEATURE_NAME is used to integrate the feature with
 // the Origin Trials framework. The framework allows the feature to be enabled
 // at runtime on a per-page basis through a signed token for the corresponding
 // feature name. Declaring the origin_trial_feature_name will cause a static
 // method to be generated in OriginTrials.h/cpp. This static method allows the
 // feature implementation to check if it is enabled for the current context.
 //
 // settable_from_internals specifies whether a feature can be set from internals.runtimeFlags, with the default
 // being false.
 
+Accelerated2dCanvas status=stable, settable_from_internals=True
 AlwaysUseComplexText status=stable
 AudioOutputDevices status=stable
 AudioVideoTracks status=experimental
 BackgroundSync status=stable
 BackspaceDefaultHandler status=test
 BroadcastChannel status=stable
 CacheIgnoreSearchOption status=experimental
 Canvas2dFixedRenderingMode status=test
 EnableCanvas2dDynamicRenderingModeSwitching status=experimental
 Canvas2dImageChromium status=experimental
@@ skipping 197 matching lines @@
 WakeLock status=experimental
 WebFontsInterventionV2With2G
 WebFontsInterventionV2WithSlow2G
 WebFontsInterventionTrigger
 WebShare status=experimental
 Worklet status=experimental
 WeakMemoryCache
 DoNotUnlockSharedBuffer
 ParseHTMLOnMainThread status=test
 SendBeaconThrowForBlobWithNonSimpleType status=experimental