Enable SwiftShader fallback on desktop Linux.

content/browser/gpu/gpu_data_manager_impl_private.cc

Index: content/browser/gpu/gpu_data_manager_impl_private.cc
diff --git a/content/browser/gpu/gpu_data_manager_impl_private.cc b/content/browser/gpu/gpu_data_manager_impl_private.cc
index 027ea48ab1729c27309aa10e453afaa69a63e870..2e3876053bc1613b49ea1c912f2bcfc87fe35311 100644
--- a/content/browser/gpu/gpu_data_manager_impl_private.cc
+++ b/content/browser/gpu/gpu_data_manager_impl_private.cc
@@ -391,6 +391,7 @@ bool GpuDataManagerImplPrivate::GpuAccessAllowed(
       // TODO(zmo): Other features might also be OK to ignore here.
       feature_diffs.erase(gpu::GPU_FEATURE_TYPE_ACCELERATED_WEBGL);
       feature_diffs.erase(gpu::GPU_FEATURE_TYPE_WEBGL2);
+      feature_diffs.erase(gpu::GPU_FEATURE_TYPE_ACCELERATED_2D_CANVAS);
     }
     if (feature_diffs.size()) {
       if (reason) {
@@ -1271,12 +1272,33 @@ void GpuDataManagerImplPrivate::EnableSwiftShaderIfNecessary() {
           switches::kDisableSoftwareRasterizer)) {
     use_swiftshader_ = true;
 
-    // Remove all previously recorded GPU info
-    gpu_info_ = gpu::GPUInfo();
-    // Set some basic info to identify the GPU as SwiftShader
+    // Adjust GPU info for SwiftShader. Most of this data only affects the
+    // chrome://gpu page, so it doesn't require querying the implementation.
+    // It is important to reset the video and image decode/encode capabilities,
+    // to prevent attempts to use them (crbug.com/702417).

[piman, 2017/04/10 23:58:55]

Could we add a method on GPUInfo to do these things? I worry that as fields are
added to that class, this function will not be maintained.

Also, could we have a test that verifies that the values returned by SwiftShader
are consistent with the values we hard-code here?

+    gpu_info_.driver_vendor = "Google Inc.";
+    gpu_info_.driver_version = "3.3.0.2";
+    gpu_info_.driver_date = "2017/04/07";
+    gpu_info_.pixel_shader_version = "3.0";
+    gpu_info_.vertex_shader_version = "3.0";
+    gpu_info_.max_msaa_samples = "4";
+    gpu_info_.gl_version = "OpenGL ES 2.0 SwiftShader";
     gpu_info_.gl_vendor = "Google Inc.";
     gpu_info_.gl_renderer = "Google SwiftShader";
+    gpu_info_.gl_extensions = "";
+    gpu_info_.gl_reset_notification_strategy = 0;
     gpu_info_.software_rendering = true;
+    gpu_info_.passthrough_cmd_decoder = false;
+    gpu_info_.supports_overlays = false;
+    gpu_info_.basic_info_state = gpu::kCollectInfoNone;
+    gpu_info_.context_info_state = gpu::kCollectInfoNone;

[piman, 2017/04/10 23:58:55]

nit: kCollectInfoSuccess for both of these, since we have effectively
"collected" the info (by hard-coding it), so we don't want to try to collect it
again.

+    gpu_info_.video_decode_accelerator_capabilities = {};
+    gpu_info_.video_encode_accelerator_supported_profiles = {};
+    gpu_info_.jpeg_decode_accelerator_supported = false;
+
+    gpu_info_.gpu.active = false;
+    for (auto& secondary_gpu : gpu_info_.secondary_gpus)
+      secondary_gpu.active = false;
 
     for (auto& status : gpu_feature_info_.status_values)
       status = gpu::kGpuFeatureStatusBlacklisted;