html_viewer: Move webcrypto to a place where html_viewer can use it.

mojo/services/html_viewer/blink_platform_impl.cc

Index: mojo/services/html_viewer/blink_platform_impl.cc
diff --git a/mojo/services/html_viewer/blink_platform_impl.cc b/mojo/services/html_viewer/blink_platform_impl.cc
index e2d6ca65cefa9c5b7587c50a3eb5ce576c7b822d..5db25fce1ea2faeaea0e41d56c2acf71d013070c 100644
--- a/mojo/services/html_viewer/blink_platform_impl.cc
+++ b/mojo/services/html_viewer/blink_platform_impl.cc
@@ -269,6 +269,10 @@ blink::WebGestureCurve* BlinkPlatformImpl::createFlingAnimationCurve(
              is_main_thread).release();
 }
 
+blink::WebCrypto* BlinkPlatformImpl::crypto() {
+  return &web_crypto_;
+}
+
 // static
 void BlinkPlatformImpl::DestroyCurrentThread(void* thread) {
   WebThreadImplForMessageLoop* impl =