Expose if we are using swiftshader via WebGraphicsContext3DProvider.

third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h

Index: third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h
diff --git a/third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h b/third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h
index e889aa321b9303d66e19545f7855bcf21e2fa485..3a5bbe6c939ae5e6ec2d4ab63e0ea31e49b9a1de 100644
--- a/third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h
+++ b/third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h
@@ -54,6 +54,10 @@ public:
     virtual GrContext* grContext() = 0;
     virtual gpu::Capabilities getCapabilities() = 0;
 
+    // Returns true if the context is driven by software emulation of GL. In
+    // this scenario, the compositor would not be using GPU.
+    virtual bool isSoftwareRendering() const = 0;
+
     virtual void setLostContextCallback(WebClosure) = 0;
     virtual void setErrorMessageCallback(WebFunction<void(const char* msg, int32_t id)>) = 0;
 };