Add sRGB mode toggle to Viewer.

tools/viewer/sk_app/Window.h

Index: tools/viewer/sk_app/Window.h
diff --git a/tools/viewer/sk_app/Window.h b/tools/viewer/sk_app/Window.h
index 3dd558e75ae2362cad4bafe648515311e06d4c1b..a898858066fa4b4b3bfa58a6fcd9754be3deb888 100644
--- a/tools/viewer/sk_app/Window.h
+++ b/tools/viewer/sk_app/Window.h
@@ -36,7 +36,7 @@ public:
         kVulkan_BackendType
     };
 
-    virtual bool attach(BackEndType attachType, int msaaSampleCount) = 0;
+    virtual bool attach(BackEndType attachType, int msaaSampleCount, bool srgb) = 0;
     void detach();
 
     // input handling
@@ -129,6 +129,9 @@ public:
     uint32_t width() { return fWidth; }
     uint32_t height() { return fHeight;  }
 
+    bool getSRGB();
+    void setSRGB(bool srgb);
+
 protected:
     Window();