Raise the loading priority of in-viewport images.

Source/core/core.gypi

 {
     'variables': {
         'core_idl_files': [
             'css/CSS.idl',
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
             'css/CSSFontFaceRule.idl',
             'css/CSSImportRule.idl',
             'css/CSSKeyframeRule.idl',
             'css/CSSKeyframesRule.idl',
@@ skipping 970 matching lines @@
             'fetch/Resource.cpp',
             'fetch/Resource.h',
             'fetch/ResourceClientWalker.h',
             'fetch/ResourceFetcher.cpp',
             'fetch/ResourceFetcher.h',
             'fetch/ResourceLoader.cpp',
             'fetch/ResourceLoader.h',
             'fetch/ResourceLoaderOptions.h',
             'fetch/ResourceLoaderSet.cpp',
             'fetch/ResourceLoaderSet.h',
+            'fetch/ResourceLoadPriorityOptimizer.cpp',
+            'fetch/ResourceLoadPriorityOptimizer.h',
             'fetch/ResourcePtr.cpp',
             'fetch/ResourcePtr.h',
             'fetch/FetchInitiatorInfo.h',
             'fetch/ScriptResource.cpp',
             'fetch/ScriptResource.h',
             'fetch/ShaderResource.cpp',
             'fetch/ShaderResource.h',
             'fetch/TextResourceDecoder.cpp',
             'fetch/TextResourceDecoder.h',
             'fetch/XSLStyleSheetResource.cpp',
@@ skipping 2337 matching lines @@
             'platform/animation/AnimationTranslationUtilTest.cpp',
             'platform/animation/TimingFunctionTestHelper.h',
             'platform/animation/TimingFunctionTestHelper.cpp',
             'platform/animation/TimingFunctionTestHelperTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'testing/UnitTestHelpers.h',
             'testing/UnitTestHelpers.cpp',
         ],
     }
 }