Bring back sRGB-write-control as a caps bit.

src/gpu/gl/GrGLCaps.cpp

Index: src/gpu/gl/GrGLCaps.cpp
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 9b12ce69c50b89ad0d66be2e6bfb15736a3ab960..ebfbf6a065ad3f79641040dc81a3a5925cc301e7 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -1457,8 +1457,7 @@ void GrGLCaps::initConfigTable(const GrGLContextInfo& ctxInfo, const GrGLInterfa
     fConfigTable[kBGRA_8888_GrPixelConfig].fSwizzle = GrSwizzle::RGBA();
 
     // We only enable srgb support if both textures and FBOs support srgb,
-    // *and* we can disable sRGB decode-on-read, to support "legacy" mode,
-    // *and* we can disable sRGB encode-on-write.
+    // *and* we can disable sRGB decode-on-read, to support "legacy" mode.
     if (kGL_GrGLStandard == standard) {
         if (ctxInfo.version() >= GR_GL_VER(3,0)) {
             fSRGBSupport = true;
@@ -1469,13 +1468,14 @@ void GrGLCaps::initConfigTable(const GrGLContextInfo& ctxInfo, const GrGLInterfa
             }
         }
         // All the above srgb extensions support toggling srgb writes
+        fSRGBWriteControl = true;
     } else {
         // See https://bug.skia.org/4148 for PowerVR issue.
         fSRGBSupport = kPowerVRRogue_GrGLRenderer != ctxInfo.renderer() &&
             (ctxInfo.version() >= GR_GL_VER(3,0) || ctxInfo.hasExtension("GL_EXT_sRGB"));
         // ES through 3.1 requires EXT_srgb_write_control to support toggling
         // sRGB writing for destinations.
-        fSRGBSupport = fSRGBSupport && ctxInfo.hasExtension("GL_EXT_sRGB_write_control");
+        fSRGBWriteControl = ctxInfo.hasExtension("GL_EXT_sRGB_write_control");
     }
     if (!ctxInfo.hasExtension("GL_EXT_texture_sRGB_decode")) {
         // To support "legacy" L32 mode, we require the ability to turn off sRGB decode: