Adding support for controlling the global sRGB SkColor switch.

Frontend change: https://codereview.chromium.org/1900233002/

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1902143002

Review URL: https://codereview.chromium.org/1902143002
diff --git a/tools/skiaserve/Request.cpp b/tools/skiaserve/Request.cpp
index 58aca84..7cbc9ef 100644
--- a/tools/skiaserve/Request.cpp
+++ b/tools/skiaserve/Request.cpp
@@ -9,6 +9,7 @@
 
 #include "SkPictureRecorder.h"
 #include "SkPixelSerializer.h"
+#include "SkPM4fPriv.h"
 #include "picture_utils.h"
 
 using namespace sk_gpu_test;
@@ -186,6 +187,11 @@
     return enableGPU(fGPUEnabled);
 }
 
+bool Request::setSRGBMode(bool enable) {
+    gTreatSkColorAsSRGB = enable;
+    return true;
+}
+
 bool Request::enableGPU(bool enable) {
     if (enable) {
         SkSurface* surface = this->createGPUSurface();
@@ -238,6 +244,7 @@
     root["mode"] = Json::Value(fGPUEnabled ? "gpu" : "cpu");
     root["drawGpuBatchBounds"] = Json::Value(fDebugCanvas->getDrawGpuBatchBounds());
     root["colorMode"] = Json::Value(fColorMode);
+    root["srgbMode"] = Json::Value(gTreatSkColorAsSRGB);
     SkDynamicMemoryWStream stream;
     stream.writeText(Json::FastWriter().write(root).c_str());