Fix crashing webcrypto fuzzers.

Use blink::Platform::CreateMainThreadAndInitialize() to create and own the main thread.

Bug: 872240
Change-Id: I53c8ad6875aecf83246f8077e03eed6482d36be4
Reviewed-on: https://chromium-review.googlesource.com/1168194
Reviewed-by: Ryan Sleevi <[email protected]>
Commit-Queue: Eric Roman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#581775}
diff --git a/components/webcrypto/fuzzer_support.cc b/components/webcrypto/fuzzer_support.cc
index 06d0acd..d4460ed0 100644
--- a/components/webcrypto/fuzzer_support.cc
+++ b/components/webcrypto/fuzzer_support.cc
@@ -26,7 +26,7 @@
   InitOnce() {
     base::CommandLine::Init(0, nullptr);
     mojo::core::Init();
-    blink::Platform::Initialize(this, CurrentThread());
+    blink::Platform::CreateMainThreadAndInitialize(this);
   }
   ~InitOnce() override {}