Add sRGB mode toggle to Viewer.

tools/viewer/sk_app/WindowContext.h

Index: tools/viewer/sk_app/WindowContext.h
diff --git a/tools/viewer/sk_app/WindowContext.h b/tools/viewer/sk_app/WindowContext.h
index 5811bedd32876216c6d2e2fa7ad123869e181c30..d48e38e7466949b07031a3dd2443231f3011e847 100644
--- a/tools/viewer/sk_app/WindowContext.h
+++ b/tools/viewer/sk_app/WindowContext.h
@@ -7,6 +7,7 @@
 #ifndef WindowContext_DEFINED
 #define WindowContext_DEFINED
 
+#include "DisplayParams.h"
 #include "GrTypes.h"
 
 class SkSurface;
@@ -28,6 +29,9 @@ public:
 
     virtual void resize(uint32_t w, uint32_t h) = 0;
 
+    virtual const DisplayParams& getDisplayParams() = 0;
+    virtual void setDisplayParams(const DisplayParams& params) = 0;
+
     virtual GrBackendContext getBackendContext() = 0;
 };