Introduce a basic Blink Scheduler

Source/platform/blink_platform.gypi

Index: Source/platform/blink_platform.gypi
diff --git a/Source/platform/blink_platform.gypi b/Source/platform/blink_platform.gypi
index c873fec1c6659278f95babe783a82c001cb61849..3ea0578fcd08fa848cc83894937dac1185139a59 100644
--- a/Source/platform/blink_platform.gypi
+++ b/Source/platform/blink_platform.gypi
@@ -297,6 +297,7 @@
       'exported/WebRTCStatsRequest.cpp',
       'exported/WebRTCStatsResponse.cpp',
       'exported/WebRTCVoidRequest.cpp',
+      'exported/WebScheduler.cpp',
       'exported/WebScrollbarImpl.cpp',
       'exported/WebScrollbarImpl.h',
       'exported/WebScrollbarThemeClientImpl.cpp',
@@ -737,6 +738,8 @@
       'plugins/PluginData.h',
       'plugins/PluginListBuilder.cpp',
       'plugins/PluginListBuilder.h',
+      'scheduler/Scheduler.cpp',
+      'scheduler/Scheduler.h',
       'scroll/FramelessScrollView.cpp',
       'scroll/FramelessScrollView.h',
       'scroll/FramelessScrollViewClient.h',
@@ -915,6 +918,7 @@
       'image-decoders/ImageDecoderTest.cpp',
       'mac/ScrollElasticityControllerTest.mm',
       'network/HTTPParsersTest.cpp',
+      'scheduler/SchedulerTest.cpp',
       'testing/ArenaTestHelpers.h',
       'testing/TreeTestHelpers.cpp',
       'testing/TreeTestHelpers.h',