First attempt to capture parser/translation errors in browser.

src/IceBrowserCompileServer.cpp

 //===- subzero/src/IceBrowserCompileServer.cpp - Browser compile server ---===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the browser-based compile server.
@@ skipping 63 matching lines @@
 int onDataCallback(const void *Data, size_t NumBytes) {
   return gCompileServer->pushInputBytes(Data, NumBytes) ? 1 : 0;
 }
 
 char *onEndCallback() {
   gCompileServer->endInputStream();
   gCompileServer->waitForCompileThread();
   // TODO(jvoung): Also return an error string, and UMA data.
   // Set up a report_fatal_error handler to grab that string.
   if (gCompileServer->getErrorCode().value()) {
-    return strdup("Some error occurred");
+    const std::string Error = gCompileServer->getErrorStream().getContents();
+    return strdup(Error.empty() ? "Some error occurred" : Error.c_str());
   }
   return nullptr;
 }
 
 struct nacl_irt_pnacl_compile_funcs SubzeroCallbacks {
   &onInitCallback, &onDataCallback, &onEndCallback
 };
 
 std::unique_ptr<llvm::raw_fd_ostream> getOutputStream(int FD) {
   if (FD <= 0)
@@ skipping 40 matching lines @@
 }
 
 void BrowserCompileServer::endInputStream() { InputStream->SetDone(); }
 
 void BrowserCompileServer::startCompileThread(int ObjFD) {
   InputStream = new llvm::QueueStreamer();
   LogStream = getOutputStream(STDOUT_FILENO);
   LogStream->SetUnbuffered();
   EmitStream = getOutputStream(ObjFD);
   EmitStream->SetBufferSize(1 << 14);
+  std::unique_ptr<StringStream> ErrStrm(new StringStream());
+  ErrorStream = std::move(ErrStrm);
   ELFStream.reset(new ELFStreamer(*EmitStream.get()));
   Ctx.reset(new GlobalContext(LogStream.get(), EmitStream.get(),
-                              ELFStream.get(), Flags));
+                              &ErrorStream->getStream(), ELFStream.get(),
+                              Flags));
   CompileThread = std::thread([this]() {
     Ctx->initParserThread();
     this->getCompiler().run(ExtraFlags, *Ctx.get(),
                             // Retain original reference, but the compiler
                             // (LLVM's MemoryObject) wants to handle deletion.
                             std::unique_ptr<llvm::DataStreamer>(InputStream));
   });
 }
 
 } // end of namespace Ice
 
 #endif // PNACL_BROWSER_TRANSLATOR