Add sRGB mode toggle to Viewer.

tools/viewer/sk_app/DisplayParams.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef DisplayParams_DEFINED
+#define DisplayParams_DEFINED
+
+#include "SkImageInfo.h"
+
+namespace sk_app {
+
+struct DisplayParams {
+    DisplayParams()
+        : fColorType(kN32_SkColorType)
+        , fProfileType(kLinear_SkColorProfileType)
+        , fMSAASampleCount(0) {}
+
+    SkColorType fColorType;
+    SkColorProfileType fProfileType;
+    int fMSAASampleCount;
+};
+
+}   // namespace sk_app
+
+#endif