Disable WebAssembly in proxy_resolver_v8.cc

Removes some potential attack surface since wasm isn't expected
as part of proxy resolution.

Change-Id: I82b6519a3d60a5577796fe0627f5750234032849
Reviewed-on: https://chromium-review.googlesource.com/c/1321578Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606073}

net/proxy_resolution/proxy_resolver_v8.cc

@@ -385,6 +385,11 @@ class SharedIsolateFactory {
         static const char kNoOpt[] = "--noopt";
         v8::V8::SetFlagsFromString(kNoOpt, strlen(kNoOpt));
 
+        // WebAssembly isn't encountered during resolution, so reduce the
+        // potential attack surface.
+        static const char kNoExposeWasm[] = "--no-expose-wasm";
+        v8::V8::SetFlagsFromString(kNoExposeWasm, strlen(kNoExposeWasm));
+
         gin::IsolateHolder::Initialize(
             gin::IsolateHolder::kNonStrictMode,
             gin::IsolateHolder::kStableV8Extras,