Disable wasm in PDF's V8 engine.

Since PDFs don't contain webassembly.

Once this lands, we should consider doing the same thing for
the proxy_resolver_v8.cc file as well.

Change-Id: If9e33defb4ea4124eefd6555a5331cfe3f0e22b4
Reviewed-on: https://chromium-review.googlesource.com/c/1321050
Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606074}

pdf/pdfium/pdfium_engine.cc

@@ -533,6 +533,9 @@ std::string GetDocumentMetadata(FPDF_DOCUMENT doc, const std::string& key) {
 gin::IsolateHolder* g_isolate_holder = nullptr;
 
 void SetUpV8() {
+  static const char kNoExposeWasm[] = "--no-expose-wasm";
+  v8::V8::SetFlagsFromString(kNoExposeWasm, strlen(kNoExposeWasm));
+
   gin::IsolateHolder::Initialize(gin::IsolateHolder::kNonStrictMode,
                                  gin::IsolateHolder::kStableV8Extras,
                                  gin::ArrayBufferAllocator::SharedInstance());