Expose if we are using swiftshader via WebGraphicsContext3DProvider.

content/renderer/webgraphicscontext3d_provider_impl.cc

Index: content/renderer/webgraphicscontext3d_provider_impl.cc
diff --git a/content/renderer/webgraphicscontext3d_provider_impl.cc b/content/renderer/webgraphicscontext3d_provider_impl.cc
index 3fc7e6e80ca21721fb404f393584e080e7e0385d..dac541f8efc1d8847a3ef6df9f71903019c2ab3d 100644
--- a/content/renderer/webgraphicscontext3d_provider_impl.cc
+++ b/content/renderer/webgraphicscontext3d_provider_impl.cc
@@ -11,8 +11,9 @@
 namespace content {
 
 WebGraphicsContext3DProviderImpl::WebGraphicsContext3DProviderImpl(
-    scoped_refptr<ContextProviderCommandBuffer> provider)
-    : provider_(std::move(provider)) {}
+    scoped_refptr<ContextProviderCommandBuffer> provider,
+    bool software_rendering)
+    : provider_(std::move(provider)), software_rendering_(software_rendering) {}
 
 WebGraphicsContext3DProviderImpl::~WebGraphicsContext3DProviderImpl() {}
 
@@ -32,6 +33,10 @@ gpu::Capabilities WebGraphicsContext3DProviderImpl::getCapabilities() {
   return provider_->ContextCapabilities();
 }
 
+bool WebGraphicsContext3DProviderImpl::isSoftwareRendering() const {
+  return software_rendering_;
+}
+
 void WebGraphicsContext3DProviderImpl::setLostContextCallback(
     blink::WebClosure c) {
   provider_->SetLostContextCallback(c.TakeBaseCallback());