webkit: Avoid use of discardable memory unless supported natively.

BUG=237681

Review URL: https://codereview.chromium.org/60273004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233187 0039d316-1c4b-4281-b951-d872f2087c98

webkit/child/webkitplatformsupport_child_impl.cc

@@ -93,6 +93,8 @@ void WebKitPlatformSupportChildImpl::didStopWorkerRunLoop(
 
 WebKit::WebDiscardableMemory*
 WebKitPlatformSupportChildImpl::allocateAndLockDiscardableMemory(size_t bytes) {
+  if (!base::DiscardableMemory::SupportedNatively())
+    return NULL;
   return WebDiscardableMemoryImpl::CreateLockedMemory(bytes).release();
 }