adds WARP support to Chromium, for Metro mode only, on Windows 8

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 fd705c8967ac20837a5d2c6b45f039d7c71b3fa2..c4fc062e42959557b5b30e4930bc2df7247bd9f9 100644
--- a/content/browser/gpu/gpu_data_manager_impl_private.cc
+++ b/content/browser/gpu/gpu_data_manager_impl_private.cc
@@ -271,7 +271,7 @@ bool GpuDataManagerImplPrivate::IsFeatureBlacklisted(int feature) const {
     return true;
   }
 #endif  // OS_CHROMEOS
-  if (use_swiftshader_) {
+  if (use_swiftshader_ || ShouldUseWarp()) {
     // Skia's software rendering is probably more efficient than going through
     // software emulation of the GPU, so use that.
     if (feature == gpu::GPU_FEATURE_TYPE_ACCELERATED_2D_CANVAS)
@@ -287,7 +287,7 @@ bool GpuDataManagerImplPrivate::IsDriverBugWorkaroundActive(int feature) const {
 }
 
 size_t GpuDataManagerImplPrivate::GetBlacklistedFeatureCount() const {
-  if (use_swiftshader_)
+  if (use_swiftshader_ || ShouldUseWarp())
     return 1;
   return blacklisted_features_.size();
 }
@@ -311,7 +311,7 @@ void GpuDataManagerImplPrivate::GetGpuProcessHandles(
 
 bool GpuDataManagerImplPrivate::GpuAccessAllowed(
     std::string* reason) const {
-  if (use_swiftshader_)
+  if (use_swiftshader_ || ShouldUseWarp())
     return true;
 
   if (!gpu_process_accessible_) {
@@ -398,6 +398,11 @@ void GpuDataManagerImplPrivate::RegisterSwiftShaderPath(
   EnableSwiftShaderIfNecessary();
 }
 
+bool GpuDataManagerImplPrivate::ShouldUseWarp() const {
+  return use_warp_ ||
+      CommandLine::ForCurrentProcess()->HasSwitch(switches::kUseWarp);
+}
+
 void GpuDataManagerImplPrivate::AddObserver(GpuDataManagerObserver* observer) {
   GpuDataManagerImpl::UnlockedSession session(owner_);
   observer_list_->AddObserver(observer);
@@ -545,7 +550,7 @@ void GpuDataManagerImplPrivate::UpdateGpuInfoHelper() {
 
 void GpuDataManagerImplPrivate::UpdateGpuInfo(const gpu::GPUInfo& gpu_info) {
   // No further update of gpu_info if falling back to SwiftShader.
-  if (use_swiftshader_)
+  if (use_swiftshader_ || ShouldUseWarp())
     return;
 
   gpu::MergeGPUInfo(&gpu_info_, gpu_info);
@@ -645,6 +650,9 @@ void GpuDataManagerImplPrivate::AppendGpuCommandLine(
       gpu_info_.driver_vendor);
   command_line->AppendSwitchASCII(switches::kGpuDriverVersion,
       gpu_info_.driver_version);
+
+  if (ShouldUseWarp())
+    command_line->AppendSwitch(switches::kUseWarp);
 }
 
 void GpuDataManagerImplPrivate::AppendPluginCommandLine(
@@ -707,6 +715,7 @@ void GpuDataManagerImplPrivate::DisableHardwareAcceleration() {
   for (int i = 0; i < gpu::NUMBER_OF_GPU_FEATURE_TYPES; ++i)
     blacklisted_features_.insert(i);
 
+  EnableWarpIfNecessary();
   EnableSwiftShaderIfNecessary();
   NotifyGpuInfoUpdate();
 }
@@ -813,6 +822,8 @@ bool GpuDataManagerImplPrivate::UpdateActiveGpu(
 }
 
 bool GpuDataManagerImplPrivate::CanUseGpuBrowserCompositor() const {
+  if (ShouldUseWarp())
+    return true;
   if (ShouldUseSwiftShader())
     return false;
   if (IsFeatureBlacklisted(gpu::GPU_FEATURE_TYPE_GPU_COMPOSITING))
@@ -859,6 +870,7 @@ GpuDataManagerImplPrivate::GpuDataManagerImplPrivate(
     : complete_gpu_info_already_requested_(false),
       observer_list_(new GpuDataManagerObserverList),
       use_swiftshader_(false),
+      use_warp_(false),
       card_blacklisted_(false),
       update_histograms_(true),
       window_count_(0),
@@ -932,6 +944,7 @@ void GpuDataManagerImplPrivate::UpdateBlacklistedFeatures(
     blacklisted_features_.insert(gpu::GPU_FEATURE_TYPE_WEBGL);
   }
 
+  EnableWarpIfNecessary();
   EnableSwiftShaderIfNecessary();
 }
 
@@ -957,6 +970,9 @@ void GpuDataManagerImplPrivate::NotifyGpuInfoUpdate() {
 }
 
 void GpuDataManagerImplPrivate::EnableSwiftShaderIfNecessary() {
+  if (ShouldUseWarp())
+    return;

[Zhenyao Mo, 2014/08/29 18:28:50]

Please add an unit test to make sure if Warp is used,
EnableSwiftShaderIfNecessary() doesn't truly enable SwiftShader.  This is not
apparent and we need to make sure people don't break it in the future.

[luken, 2014/08/29 23:34:03]

Done.

+
   if (!GpuAccessAllowed(NULL) ||
       blacklisted_features_.count(gpu::GPU_FEATURE_TYPE_WEBGL)) {
     if (!swiftshader_path_.empty() &&
@@ -966,6 +982,15 @@ void GpuDataManagerImplPrivate::EnableSwiftShaderIfNecessary() {
   }
 }
 
+void GpuDataManagerImplPrivate::EnableWarpIfNecessary() {
+#if defined(OS_WIN)
+  // We should only use WARP if we are unable to use the regular GPU for
+  // compositing, and if we should fall back.
+  use_warp_ =  !CanUseGpuBrowserCompositor() &&
+      gpu::ShouldFallbackToWarp();
+#endif
+}
+
 std::string GpuDataManagerImplPrivate::GetDomainFromURL(
     const GURL& url) const {
   // For the moment, we just use the host, or its IP address, as the