Add control of the sRGB global hack flag in SampleApp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1893313006

Review URL: https://codereview.chromium.org/1893313006
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 12580cb..df091ae 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -22,6 +22,7 @@
 #include "SkPaintFilterCanvas.h"
 #include "SkPicture.h"
 #include "SkPictureRecorder.h"
+#include "SkPM4fPriv.h"
 #include "SkStream.h"
 #include "SkSurface.h"
 #include "SkTemplates.h"
@@ -934,6 +935,8 @@
     itemID = fAppMenu->appendList("ColorType", "ColorType", sinkID, 0,
                                   gConfig[0].fName, gConfig[1].fName, gConfig[2].fName, nullptr);
     fAppMenu->assignKeyEquivalentToItem(itemID, 'C');
+    itemID = fAppMenu->appendSwitch("sRGB SkColor", "sRGB SkColor", sinkID, gTreatSkColorAsSRGB);
+    fAppMenu->assignKeyEquivalentToItem(itemID, 'S');
 
     itemID = fAppMenu->appendList("Device Type", "Device Type", sinkID, 0,
                                   "Raster",
@@ -1649,7 +1652,8 @@
         SkOSMenu::FindListIndex(evt, "Hinting", &fHintingState) ||
         SkOSMenu::FindSwitchState(evt, "Clip", &fUseClip) ||
         SkOSMenu::FindSwitchState(evt, "Zoomer", &fShowZoomer) ||
-        SkOSMenu::FindSwitchState(evt, "Magnify", &fMagnify))
+        SkOSMenu::FindSwitchState(evt, "Magnify", &fMagnify) ||
+        SkOSMenu::FindSwitchState(evt, "sRGB SkColor", &gTreatSkColorAsSRGB))
     {
         this->inval(nullptr);
         this->updateTitle();
@@ -2158,6 +2162,10 @@
 
     title.appendf(" %s", find_config_name(this->info()));
 
+    if (gTreatSkColorAsSRGB) {
+        title.append(" sRGB");
+    }
+
     this->setTitle(title.c_str());
 }