Don't crash when main.dart is a 404.

Ideally we would show a failwhale or some such, but
I don't know how we would bundle that file with our
APK yet.

Fixes https://github.com/domokit/mojo/issues/228

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1182633002.

engine/core/script/dart_controller.cc

@@ -119,7 +119,9 @@ void DartController::DidLoadMainLibrary(KURL url) {
 
   Dart_Handle library = Dart_LookupLibrary(
       StringToDart(dart_state(), url.string()));
-  CHECK(!LogIfError(library));
+  // TODO(eseidel): We need to load a 404 page instead!
+  if (LogIfError(library))
+    return;
   DartInvokeAppField(library, ToDart("main"), 0, nullptr);
 }
 

engine/core/script/dart_loader.cc

@@ -239,6 +239,11 @@ void DartLoader::WaitForDependencies(
 }
 
 void DartLoader::LoadLibrary(const KURL& url, mojo::URLResponsePtr response) {
+  if (response && response->status_code >= 400) {
+    LOG(ERROR) << url.string().utf8().data()
+        << " failed with " << response->status_code;
+  }
+
   const auto& result = pending_libraries_.add(url.string(), nullptr);
   if (result.isNewEntry) {
     OwnPtr<Job> job = adoptPtr(new ImportJob(this, url));

services/oknet/src/org/domokit/oknet/UrlLoaderImpl.java

@@ -76,9 +76,14 @@ public class UrlLoaderImpl implements UrlLoader {
                     buffer.put(tmp);
                     mProducer.endWriteData(result == -1 ? 0 : result);
                 } catch (MojoException e) {
-                    if (e.getMojoResult() != MojoResult.SHOULD_WAIT)
-                        throw e;
+                    // No one read the pipe, they just closed it.
+                    if (e.getMojoResult() == MojoResult.FAILED_PRECONDITION) {
+                        break;
+                    } else if (e.getMojoResult() == MojoResult.SHOULD_WAIT) {
                         mCore.wait(mProducer, Core.HandleSignals.WRITABLE, -1);
+                    } else {
+                        throw e;
+                    }
                 } catch (IOException e) {
                     Log.e(TAG, "mSource.read failed", e);
                     break;