Revert "webgl: gpu workaround to turn off MSAA"

This reverts commit 4efc495c.

Reason for revert: Driver was fixed so this is no longer an issue.

Original change's description:
> webgl: gpu workaround to turn off MSAA
>
> PowerVR.*GX6250 gpu is producing artifacts when
> rendering with a context that has antialias set true.
>
> Bug: 1038671, b:148280161
> Change-Id: I79081f342bac2531e9d6d43a57939e3c5f8fc0e6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2019939
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Reviewed-by: Kenneth Russell <kbr@chromium.org>
> Commit-Queue: Kentaro Hara <haraken@chromium.org>
> Auto-Submit: Fritz Koenig <frkoenig@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#735217}

TBR=frkoenig@chromium.org,kbr@chromium.org,haraken@chromium.org

Bug: 1038671, b:148280161
Change-Id: I2e3ace6578fc90b26b5f180f388a6c80f56a0f63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036400
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738001}

content/renderer/webgraphicscontext3d_provider_impl.cc

@@ -110,8 +110,6 @@ WebGraphicsContext3DProviderImpl::GetWebglPreferences() const {
       } else {
         prefs.anti_aliasing_mode = blink::kAntialiasingModeUnspecified;
       }
-    } else if (gpu_feature_info.IsWorkaroundEnabled(WEBGL_MSAA_IS_BROKEN)) {
-      prefs.anti_aliasing_mode = blink::kAntialiasingModeNone;
     }
 
     // Set default context limits for WebGL.

gpu/config/gpu_driver_bug_list.json

@@ -3515,22 +3515,6 @@
         "limit_d3d11_video_decoder_to_11_0"
       ]
     },
-    {
-      "id": 330,
-      "cr_bugs": [1038671],
-      "description": "WebGL MSAA for PowerVR.*GX6250 context lost with GL_UNKNOWN_CONTEXT_RESET_KHR",
-      "os": {
-        "type": "chromeos"
-      },
-      "gl_vendor": "Imagination.*",
-      "gl_renderer": "PowerVR.*GX6250",
-      "features": [
-        "webgl_msaa_is_broken"
-      ],
-      "disabled_extensions": [
-        "GL_EXT_multisampled_render_to_texture"
-      ]
-    },
     {
       "id": 331,
       "cr_bugs": [1046462],

gpu/config/gpu_workaround_list.txt

@@ -120,4 +120,3 @@ use_unused_standard_shared_blocks
 use_virtualized_gl_contexts
 validate_multisample_buffer_allocation
 wake_up_gpu_before_drawing
-webgl_msaa_is_broken