[devtools] Support different encodings for Page.CaptureScreenshot.

ui/snapshot/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 component("snapshot") {
   sources = [
     "screenshot_grabber.cc",
     "screenshot_grabber.h",
     "screenshot_grabber_observer.h",
+    "snapshot.cc",
     "snapshot.h",
     "snapshot_android.cc",
     "snapshot_async.cc",
     "snapshot_async.h",
     "snapshot_aura.cc",
     "snapshot_export.h",
     "snapshot_ios.mm",
     "snapshot_mac.mm",
   ]
 
@@ skipping 69 matching lines @@
     deps += [
       "//ui/aura:test_support",
       "//ui/compositor",
       "//ui/compositor:test_support",
       "//ui/wm",
     ]
   } else {
     sources -= [ "snapshot_aura_unittest.cc" ]
   }
 }