Added Dartium changes onto 45.0.2454.104

Source/bindings/core/dart/DartApplicationLoader.cpp

+// Copyright (c) 2009, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "config.h"
+#include "bindings/core/dart/DartApplicationLoader.h"
+
+#include "core/FetchInitiatorTypeNames.h"
+#include "bindings/core/dart/DartDOMWrapper.h"
+#include "bindings/core/dart/DartInspectorTimeline.h"
+#include "bindings/core/dart/DartScriptDebugServer.h"
+#include "bindings/core/dart/DartService.h"
+#include "bindings/core/dart/DartUtilities.h"
+#if defined(ENABLE_DART_NATIVE_EXTENSIONS)
+#include "bindings/core/dart/shared_lib/DartNativeExtensions.h"
+#endif
+#include "bindings/core/v8/ScriptSourceCode.h"
+#include "core/dom/Document.h"
+#include "core/dom/Element.h"
+#include "core/dom/ScriptLoader.h"
+#include "core/dom/ScriptLoaderClient.h"
+#include "core/fetch/CachedMetadata.h"
+#include "core/fetch/FetchRequest.h"
+#include "core/fetch/ResourceClient.h"
+#include "core/fetch/ResourceFetcher.h"
+#include "core/fetch/ScriptResource.h"
+#include "core/frame/LocalDOMWindow.h"
+#include "core/frame/LocalFrame.h"
+#include "core/html/HTMLScriptElement.h"
+#include "core/inspector/ScriptCallStack.h"
+#include "core/svg/SVGScriptElement.h"
+
+#include <dart_api.h>
+#include <dart_mirrors_api.h>
+
+namespace blink {
+
+// FIXME(vsm): Define this in a central place.
+static const unsigned dartTypeID = 0xDAADDAAD;
+
+PassRefPtr<DartScriptInfo> DartScriptInfo::create(PassRefPtr<Element> scriptElement)
+{
+    RefPtr<DartScriptInfo> scriptInfo = adoptRef(new DartScriptInfo(scriptElement));
+    if (scriptInfo->loader())
+        return scriptInfo;
+    return nullptr;
+}
+
+String DartScriptInfo::sourceAttributeValue() const
+{
+    return m_client->sourceAttributeValue();
+}
+
+String DartScriptInfo::typeAttributeValue() const
+{
+    return m_client->typeAttributeValue();
+}
+
+String DartScriptInfo::scriptContent()
+{
+    return m_loader->scriptContent();
+}
+
+void DartScriptInfo::dispatchErrorEvent()
+{
+    m_loader->dispatchErrorEvent();
+}
+
+WTF::OrdinalNumber DartScriptInfo::startLineNumber()
+{
+    return m_loader->startLineNumber();
+}
+
+ScriptLoader* DartScriptInfo::loader()
+{
+    return m_loader;
+}
+
+Document* DartScriptInfo::ownerDocument()
+{
+    return m_element->ownerDocument();
+}
+
+String DartScriptInfo::url()
+{
+    String scriptURL = sourceAttributeValue();
+    KURL ownerURL = ownerDocument()->url();
+    return scriptURL.isEmpty() ? ownerURL : KURL(ownerURL, scriptURL);
+}
+
+DartScriptInfo::DartScriptInfo(PassRefPtr<Element> element)
+{
+    m_element = element;
+    if (m_element->document().isHTMLDocument()) {
+        HTMLScriptElement* scriptElement = static_cast<HTMLScriptElement*>(m_element.get());
+        m_loader = scriptElement->loader();
+        m_client = static_cast<ScriptLoaderClient*>(scriptElement);
+    } else if (m_element->document().isSVGDocument()) {
+        SVGScriptElement* scriptElement = static_cast<SVGScriptElement*>(m_element.get());
+        m_loader = scriptElement->loader();
+        m_client = static_cast<ScriptLoaderClient*>(scriptElement);
+    } else {
+        // Invalid script element.
+        m_loader = 0;
+        m_client = 0;
+        m_element = nullptr;
+    }
+}
+
+void DartApplicationLoader::Callback::reportError(const String& error, const String& url)
+{
+    m_originDocument->logExceptionToConsole(error + ": " + url, 0, url, 0, 0, nullptr);
+    if (m_scriptInfo)
+        m_scriptInfo->loader()->dispatchErrorEvent();
+}
+
+ResourcePtr<ScriptResource> DartApplicationLoader::Callback::requestScript(FetchRequest& request)
+{
+    return m_originDocument->fetcher()->fetchScript(request);
+}
+
+Document* DartApplicationLoader::Callback::document()
+{
+    return m_scriptInfo ? m_scriptInfo->ownerDocument() : m_originDocument;
+}
+
+DartApplicationLoader::DartApplicationLoader(
+    Document* document,
+    bool domEnabled)
+    : m_isolate(0)
+    , m_originDocument(document)
+    , m_loadCallback(nullptr)
+    , m_domEnabled(domEnabled)
+    , m_cacheable(false)
+    , m_state(Uninitialized)
+    , m_snapshotMode(SnapshotOff)
+{
+    ASSERT(m_originDocument);
+
+    DEFINE_STATIC_LOCAL(String, setting, (getenv("DART_SNAPSHOT_MODE")));
+    if (!setting.isNull()) {
+        if (setting == "all")
+            m_snapshotMode = SnapshotAll;
+        else if (setting == "off")
+            m_snapshotMode = SnapshotOff;
+        else if (setting == "single")
+            m_snapshotMode = SnapshotSingle;
+        else
+            DartUtilities::reportProblem(m_originDocument, String("Invalid DART_SNAPSHOT_MODE: ") + setting);
+    }
+}
+
+void DartApplicationLoader::addRequest(PassRefPtr<DartScriptInfo> scriptInfo)
+{
+    // FIXME(vsm): Temporary support to load extra Dart libraries via HTML imports before we encounter the main
+    // script. In the future, this should map to deferred loading.
+    RELEASE_ASSERT(m_state == Uninitialized);
+    m_htmlImportedScripts.append(scriptInfo);
+}
+
+void DartApplicationLoader::initialize(Dart_Isolate isolate, const String& scriptUrl, PassRefPtr<Callback> loadCallback)
+{
+    RELEASE_ASSERT(m_state == Uninitialized && !m_isolate);
+    m_isolate = isolate;
+    m_loadCallback = loadCallback;
+
+    Document* document = m_loadCallback->document();
+
+    m_scriptUrl = KURL(document->baseURL(), scriptUrl);
+    m_scriptUrlString = m_scriptUrl.string();
+
+    RELEASE_ASSERT(m_isolate == isolate);
+    Dart_EnterIsolate(isolate);
+
+    DartDOMData* domData = DartDOMData::current();
+    if (!domData->packageRoot()) {
+        m_packageRoot = String();
+    } else {
+        m_packageRoot = String(domData->packageRoot());
+    }
+    // Associate application loader with current isolate, so we can retrieve it in libraryTagHandlerCallback.
+    domData->setApplicationLoader(this);
+    Dart_Handle ALLOW_UNUSED result = Dart_SetLibraryTagHandler(&libraryTagHandlerCallback);
+    ASSERT(!Dart_IsError(result));
+
+    // FIXME: Stay in isolate for processing below.
+    Dart_ExitIsolate();
+    m_state = Initialized;
+}
+
+void DartApplicationLoader::processRequests(Dart_Isolate isolate, const ScriptSourceCode& sourceCode, PassRefPtr<Callback> loadCallback)
+{
+    DART_START_TIMER();
+    const String& scriptUrl = sourceCode.url();
+    initialize(isolate, scriptUrl, loadCallback);
+    DART_RECORD_TIMER("  DartApplicationLoader::initialize took");
+
+    m_state = Fetching;
+
+    // Check for cached snapshot.
+    ScriptResource* scriptResource = sourceCode.resource();
+    if (scriptResource && m_snapshotMode != SnapshotOff) {
+        // This is cacheable if there is a resource we can cache the snapshot on.
+        m_cacheable = true;
+        CachedMetadata* cachedMetadata = scriptResource->cachedMetadata(dartTypeID);
+        if (cachedMetadata) {
+            loadScriptFromSnapshot(sourceCode.url(), reinterpret_cast<const uint8_t*>(cachedMetadata->data()), cachedMetadata->size());
+            return;
+        }
+    }
+
+    // Set up root library for main DOM isolate.
+    {
+        DartIsolateScope isolateScope(m_isolate);
+        DartApiScope apiScope;
+
+        ASSERT(Dart_IsNull(Dart_RootLibrary()));
+
+        Document* document = m_loadCallback->document();
+        const String& source = sourceCode.source();
+        int lineNumber = sourceCode.startLine();
+
+        // Use zero-based counting instead of one-based.
+        lineNumber = (lineNumber <= 0) ? 0 : lineNumber - 1;
+
+        String canonical = KURL(document->url(), scriptUrl).string();
+        m_pendingLibraries.add(canonical);
+        process(canonical, source, lineNumber);
+
+        // Any problem loading main script we're done.
+        if (m_state == Error)
+            return;
+
+        RELEASE_ASSERT(m_state >= Loading);
+    }
+
+    // FIXME(vsm): This will go away.
+    // Load HTML imported dart scripts.
+    while (!m_htmlImportedScripts.isEmpty()) {
+        RefPtr<DartScriptInfo> script = m_htmlImportedScripts.takeFirst();
+        const String& src = script->sourceAttributeValue();
+        const String& url = script->url();
+        if (src.isEmpty()) {
+            // Inline script.
+            ASSERT(!m_pendingLibraries.contains(url));
+            m_pendingLibraries.add(url);
+            intptr_t lineOffset = script->startLineNumber().zeroBasedInt();
+            // Blink gives generated script tags an invalid start line.
+            if (lineOffset < 0)
+                lineOffset = 0;
+            process(script->url(), script->scriptContent(), lineOffset);
+        } else {
+            // Canonicalize the src attribute url.
+            String canonical = KURL(script->ownerDocument()->url(), src).string();
+
+            // Check if this was loaded by an earlier script.
+            {
+                DartIsolateScope isolateScope(m_isolate);
+                DartApiScope apiScope;
+                Dart_Handle library = Dart_LookupLibrary(DartUtilities::safeStringToDartString(canonical));
+                if (!Dart_IsError(library))
+                    continue;
+            }
+
+            // Request if we don't have the script or haven't already requested it.
+            if (!m_pendingLibraries.contains(canonical)) {
+                m_pendingLibraries.add(canonical);
+                fetchScriptResource(canonical);
+            }
+        }
+    }
+
+    // FIXME(vsm): Once m_htmlImportedScripts goes away, we should be able to delete this.
+    // Processing HTML imports may be made the app ready without running.
+    RELEASE_ASSERT(m_state == Error || m_state >= Loading);
+    if (ready() && m_state == Loading) {
+        m_state = Ready;
+        // All dependences are in.
+        m_loadCallback->ready();
+    }
+
+    DART_RECORD_TIMER("  DartApplicationLoader::processRequests took");
+}
+
+void DartApplicationLoader::processSingleRequest(Dart_Isolate isolate, const String& scriptUrl, PassRefPtr<Callback> loadCallback)
+{
+    initialize(isolate, scriptUrl, loadCallback);
+    // Use the resolved scriptUrl.
+    m_pendingLibraries.add(m_scriptUrlString);
+    m_state = Fetching;
+    fetchScriptResource(m_scriptUrlString);
+}
+
+void DartApplicationLoader::load(PassRefPtr<DartErrorEventDispatcher> errorEventDispatcher)
+{
+    RELEASE_ASSERT(m_state == Ready || m_state == DeferredReady);
+
+    m_errorEventDispatcher = errorEventDispatcher;
+
+    DartIsolateScope isolateScope(m_isolate);
+    DartApiScope dartApiScope;
+    bool completeFutures = false;
+
+    // Finalize classes and complete futures if there are any deferred loads.
+    if (m_state == DeferredReady) {
+        // We have already invoked the entry point on the main script URL at
+        // this point we will start running dart code again.
+        m_state = Running;
+        completeFutures = true;
+    } else {
+        RELEASE_ASSERT(m_state == Ready);
+    }
+
+    {
+        V8Scope v8scope(DartDOMData::current());
+        Dart_Handle result = Dart_FinalizeLoading(completeFutures);
+
+        if (completeFutures && m_domEnabled) {
+            // Call this after Dart_FinalizeLoading so that everything is ready.
+            Timeline timeline(m_originDocument->frame(), String("notifyDebugServerDeferredReady@") + m_scriptUrlString);
+            DartScriptDebugServer::shared().deferredReady();
+        }
+
+        if (Dart_IsError(result)) {
+            reportDartError(result);
+            return;
+        }
+    }
+    // Invoke the entry point on the main script URL if it has not yet been
+    // invoked.
+    if (m_state == Ready) {
+        // Call the entry point on the main script URL.
+        callEntryPoint();
+    }
+}
+
+void DartApplicationLoader::loadScriptFromSnapshot(const String& url, const uint8_t* snapshot, intptr_t snapshotSize)
+{
+    DART_START_TIMER();
+    RELEASE_ASSERT(m_state == Fetching);
+
+    Timeline timeline(m_originDocument->frame(), String("loadSnapshot@") + m_scriptUrlString);
+    m_scriptUrlString = url;
+    DartIsolateScope isolateScope(m_isolate);
+    DartApiScope apiScope;
+    Dart_Handle result = Dart_LoadScriptFromSnapshot(snapshot, snapshotSize);
+    if (Dart_IsError(result)) {
+        reportDartError(result);
+        return;
+    }
+
+    m_state = Ready;
+    m_loadCallback->ready();
+    DART_RECORD_TIMER("  DartApplicationLoader::loadScriptFromSnapshot took");
+}
+
+void DartApplicationLoader::callEntryPoint()
+{
+    RELEASE_ASSERT(m_state == Ready);
+
+    Timeline timeline(m_originDocument->frame(), String("callEntryPoint@") + m_scriptUrlString);
+
+    if (m_cacheable) {
+        // Snapshot single-script applications.
+        ResourceFetcher* loader = m_originDocument->fetcher();
+        FetchRequest request(m_originDocument->completeURL(m_scriptUrlString), FetchInitiatorTypeNames::document);
+        ResourcePtr<ScriptResource> scriptResource = loader->fetchScript(request);
+
+        // Check if already snapshotted.
+        if (scriptResource && !scriptResource->cachedMetadata(dartTypeID)) {
+            uint8_t* buffer;
+            intptr_t size;
+            Dart_Handle result = Dart_CreateScriptSnapshot(&buffer, &size);
+            if (Dart_IsError(result)) {
+                reportDartError(result);
+                // FIXME: exiting early might be not the best option if error is due to snapshot
+                // creation proper (and not due to compilation), even though it's unlikely.
+                // Consider other options like Dart_CompileAll.
+                return;
+            }
+
+            Vector<uint8_t>* snapshot = DartDOMData::current()->applicationSnapshot();
+            ASSERT(snapshot->isEmpty());
+            snapshot->append(buffer, size);
+
+            // Write the snapshot.
+            scriptResource->setCachedMetadata(dartTypeID, reinterpret_cast<const char*>(buffer), size);
+        }
+    }
+
+    m_state = Running;
+
+    if (m_domEnabled) {
+        Timeline timeline(m_originDocument->frame(), String("notifyDebugServer@") + m_scriptUrlString);
+        DartScriptDebugServer::shared().isolateLoaded();
+    }
+
+    if (m_domEnabled) {
+        V8Scope v8scope(DartDOMData::current());
+        Dart_Handle mainLibrary = topLevelLibrary();
+
+        logObservatoryInformation();
+
+        // Trampoline to invoke main.
+        // FIXME: Use the page library instead. To do this, we need to import each script tag's library into the page
+        // with a unique prefix to ensure a secondary script doesn't define a main.
+        String trampolineUrl = m_scriptUrlString + "$trampoline";
+        Dart_Handle trampoline = Dart_LoadLibrary(DartUtilities::safeStringToDartString(trampolineUrl), Dart_NewStringFromCString(""), 0, 0);
+        Dart_LibraryImportLibrary(trampoline, mainLibrary, Dart_Null());
+
+        Dart_Handle result = Dart_FinalizeLoading(false);
+        if (Dart_IsError(result)) {
+            DartUtilities::reportProblem(m_originDocument, result, m_scriptUrlString);
+        }
+
+        // FIXME: Settle on proper behavior here. We have not determined exactly when
+        // or how often we'll call the entry point.
+        Dart_Handle entryPoint = Dart_NewStringFromCString("main");
+        Dart_Handle main = Dart_LookupFunction(trampoline, entryPoint);
+        if (!Dart_IsNull(main)) {
+            // FIXME: Avoid relooking up main.
+            Dart_Handle result = Dart_Invoke(trampoline, entryPoint, 0, 0);
+            if (Dart_IsError(result)) {
+                DartUtilities::reportProblem(m_originDocument, result, m_scriptUrlString);
+            }
+        }
+
+    }
+}
+
+
+void DartApplicationLoader::logObservatoryInformation()
+{
+    const char* serverIp = DartService::GetServerIP();
+    const int serverPort = DartService::GetServerPort();
+    String message = String::format("Observatory listening at http://%s:%d/", serverIp, serverPort);
+    m_originDocument->addConsoleMessage(
+        ConsoleMessage::create(JSMessageSource, InfoMessageLevel, message));
+}
+
+
+void DartApplicationLoader::validateUrlLoaded(const String& url)
+{
+    RELEASE_ASSERT(m_state == Running);
+
+    DartIsolateScope isolateScope(m_isolate);
+    DartApiScope apiScope;
+
+    Dart_Handle library = Dart_LookupLibrary(DartUtilities::safeStringToDartString(url));
+    if (!Dart_IsNull(library)) {
+        DartUtilities::reportProblem(m_originDocument, "URL must be imported by main Dart script: " + url);
+    }
+}
+
+Dart_Handle DartApplicationLoader::topLevelLibrary()
+{
+    Dart_Handle library = Dart_LookupLibrary(DartUtilities::safeStringToDartString(m_scriptUrlString));
+    ASSERT(!Dart_IsError(library));
+    return library;
+}
+
+void DartApplicationLoader::findDependences(const String& url, const String& source, intptr_t lineNumber)
+{
+    ASSERT(m_pendingLibraries.contains(url) || m_pendingSource.contains(url));
+
+    DartIsolateScope isolateScope(m_isolate);
+    DartApiScope dartApiScope;
+
+    if (m_pendingLibraries.contains(url)) {
+        processLibrary(url, source, lineNumber);
+    } else {
+        ASSERT(m_pendingSource.contains(url));
+        processSource(url, source, lineNumber);
+    }
+}
+
+void DartApplicationLoader::processLibrary(const String& url, const String& source, intptr_t lineNumber)
+{
+    ASSERT(m_pendingLibraries.contains(url));
+
+    Dart_Handle result;
+    if (m_state == Fetching) {
+        // A spawned isolate.
+        m_state = Loading;
+        result = Dart_LoadScript(DartUtilities::safeStringToDartString(url), DartUtilities::convertSourceString(source), lineNumber, 0);
+    } else {
+        result = Dart_LoadLibrary(DartUtilities::safeStringToDartString(url), DartUtilities::convertSourceString(source), lineNumber, 0);
+    }
+    if (Dart_IsError(result))
+        reportError(result, url);
+
+    m_pendingLibraries.remove(url);
+}
+
+void DartApplicationLoader::processSource(const String& url, const String& source, intptr_t lineNumber)
+{
+    ASSERT(m_pendingSource.contains(url));
+    HandleSet* importers = m_pendingSource.take(url);
+    for (HandleSet::iterator i = importers->begin(); i != importers->end(); ++i) {
+        Dart_Handle persistent = *i;
+        Dart_Handle library = Dart_HandleFromPersistent(persistent);
+        Dart_DeletePersistentHandle(persistent);
+
+        Dart_Handle result = Dart_LoadSource(library, DartUtilities::safeStringToDartString(url), DartUtilities::convertSourceString(source), lineNumber, 0);
+        if (Dart_IsError(result))
+            reportError(result, url);
+    }
+    delete importers;
+}
+
+void DartApplicationLoader::process(const String& url, const String& source, intptr_t lineNumber)
+{
+    if (m_state == Error)
+        return;
+
+    if (url != m_scriptUrlString && m_snapshotMode != SnapshotAll)
+        m_cacheable = false;
+
+    RELEASE_ASSERT(m_state == Fetching || m_state == Loading || m_state == DeferredLoading);
+    findDependences(url, source, lineNumber);
+    RELEASE_ASSERT(m_state == Error || m_state == Loading || m_state == DeferredLoading);
+
+    if (ready()) {
+        m_state = (m_state == Loading) ? Ready : DeferredReady;
+        // All dependences are in.
+        m_loadCallback->ready();
+    }
+}
+
+Dart_Handle DartApplicationLoader::libraryTagHandlerCallback(Dart_LibraryTag tag, Dart_Handle library, Dart_Handle urlHandle)
+{
+    ASSERT(Dart_CurrentIsolate());
+    ASSERT(Dart_IsLibrary(library));
+
+    const String url = DartUtilities::toString(urlHandle);
+
+    if (tag == Dart_kCanonicalizeUrl) {
+        if (url.startsWith("dart:")) {
+            if (url == "dart:io" || url == "dart:_builtin" || url == "dart:vmserviceio") {
+                // We do not allow Dartium isolates to import 'dart:io' and 'dart:_builtin'.
+                return Dart_NewApiError("The requested built-in library is not available on Dartium.");
+            }
+        }
+        // If a dart application calls spawnUri, the DartVM will call this
+        // libraryTagHandler to canonicalize the url.
+        // DartDOMData::current()->scriptLoader() may be 0 at this point.
+        return DartUtilities::canonicalizeUrl(library, urlHandle, url);
+    }
+
+    if (url.startsWith("dart:")) {
+        // All supported system URLs are already built-in and shouldn't get to this point.
+        return Dart_NewApiError("The requested built-in library is not available on Dartium.");
+    }
+
+    RefPtr<DartApplicationLoader> loader = DartDOMData::current()->applicationLoader();
+    ASSERT(loader);
+    // We can only handle requests in one of the following states.
+    if (loader->m_state == Error)
+        return Dart_NewApiError("The isolate is in an invalid state.");
+    RELEASE_ASSERT(loader->m_state == Fetching || loader->m_state == Loading || loader->m_state == Running || loader->m_state == DeferredLoading);
+
+
+    // Fetch non-system URLs.
+    if (tag == Dart_kImportTag) {
+        if (loader->m_pendingLibraries.contains(url))
+            return Dart_True();
+#if defined(ENABLE_DART_NATIVE_EXTENSIONS)
+        if (url.startsWith("dart-ext:")) {
+            return DartNativeExtensions::loadExtension(url, library);
+        }
+#endif
+        loader->m_pendingLibraries.add(url);
+    } else if (tag == Dart_kSourceTag) {
+        Dart_PersistentHandle importer = Dart_NewPersistentHandle(library);
+        HandleSet* importers;
+        if (loader->m_pendingSource.contains(url)) {
+            // We have already requested this url. It is a part of more than one library.
+            importers = loader->m_pendingSource.get(url);
+            importers->append(importer);
+            return Dart_True();
+        }
+        importers = new HandleSet();
+        loader->m_pendingSource.add(url, importers);
+        importers->append(importer);
+    } else {
+        ASSERT_NOT_REACHED();
+    }
+
+    // If the isolate is running, this is part of a deferred load request.
+    if (loader->m_state == Running)
+        loader->m_state = DeferredLoading;
+    loader->fetchScriptResource(url);
+    return Dart_True();
+}
+
+class ScriptLoadedCallback : public ScriptResourceClient {
+public:
+    ScriptLoadedCallback(String url, PassRefPtr<DartApplicationLoader> loader, ResourcePtr<ScriptResource> scriptResource)
+        : m_url(url)
+        , m_loader(loader)
+        , m_scriptResource(scriptResource)
+    {
+    }
+
+    virtual void notifyFinished(Resource* cachedResource)
+    {
+        ASSERT(cachedResource->type() == Resource::Script);
+        ASSERT(cachedResource == m_scriptResource.get());
+        ASSERT(WTF::isMainThread());
+
+        if (cachedResource->errorOccurred()) {
+            m_loader->reportError(String("An error occurred loading file"), m_url);
+        } else if (cachedResource->wasCanceled()) {
+            // FIXME: shall we let VM know, so it can inform application some of its
+            // resources cannot be loaded?
+            m_loader->reportError(String("File request cancelled"), m_url);
+        } else {
+            ScriptSourceCode sourceCode(m_scriptResource.get());
+
+            // Use the original url associated with the Script so that
+            // redirects do not break the DartScriptLoader.
+            // FIXME: is this the correct behavior? This functionality is
+            // very convenient when you want the source file to act as if
+            // it was from the original location but that isn't always
+            // what the user expects.
+            m_loader->process(m_url, sourceCode.source(), 0);
+        }
+
+        m_scriptResource->removeClient(this);
+        delete this;
+    }
+
+private:
+    String m_url;
+    RefPtr<DartApplicationLoader> m_loader;
+    ResourcePtr<ScriptResource> m_scriptResource;
+};
+
+static String resolveUrl(String mainLibraryURL, const String& url, const String& packageRootOverride)
+{
+    if (!url.startsWith("package:") || url.startsWith("package://"))
+        return url;
+
+    String packageRoot;
+    String packageUrl;
+    if (!packageRootOverride.isNull()) {
+        // Resolve with respect to the override. Append a
+        // slash to ensure that resolution is against this
+        // path and not its parent.
+        packageRoot = packageRootOverride + "/";
+        // Strip the 'package:' prefix.
+        packageUrl = url.substring(8);
+        if (!(packageRoot.startsWith("file:") || packageRoot.startsWith("http:") || packageRoot.startsWith("https:"))) {
+            return packageRoot + packageUrl;
+        }
+    } else {
+        // Resolve with respect to the entry point's URL. Note, the
+        // trailing file name in the entry point URL (e.g.,
+        // 'rootpath/mainapp.dart') is stripped by the KURL
+        // constructor below.
+        packageRoot = mainLibraryURL;
+        packageUrl = String("packages/") + url.substring(8);
+    }
+    return KURL(KURL(KURL(), packageRoot), packageUrl).string();
+}
+
+void DartApplicationLoader::fetchScriptResource(const String& url)
+{
+    // Request loading of script dependencies.
+    FetchRequest request(m_loadCallback->completeURL(resolveUrl(m_scriptUrl, url, m_packageRoot)),
+        FetchInitiatorTypeNames::document, "utf8");
+    // FIXME: what about charset for this script, maybe use charset of initial script tag?
+    ResourcePtr<ScriptResource> scriptResource = m_loadCallback->requestScript(request);
+    if (scriptResource) {
+        scriptResource->addClient(new ScriptLoadedCallback(m_loadCallback->completeURL(url), this, scriptResource));
+    } else {
+        m_loadCallback->reportError(String("File request error"), url);
+    }
+}
+
+// FIXME(vsm): Merge these functions below. We need to be careful about where the error is dispatched.
+void DartApplicationLoader::scriptLoadError(String failedUrl)
+{
+    if (m_state < Running)
+        m_state = Error;
+    // FIXME: try to dig out line number, -1 for now.
+    if (failedUrl.startsWith(String("dart:"))) {
+        m_originDocument->logExceptionToConsole(String("The built-in library '") + failedUrl + String("' is not available on Dartium."), 0, m_scriptUrlString, -1, 0, nullptr);
+    } else {
+        m_originDocument->logExceptionToConsole(String("Failed to load a file ") + failedUrl, 0, m_scriptUrlString, -1, 0, nullptr);
+    }
+    RELEASE_ASSERT(m_errorEventDispatcher);
+    m_errorEventDispatcher->dispatchErrorEvent();
+}
+
+void DartApplicationLoader::reportDartError(Dart_Handle error)
+{
+    if (m_state < Running)
+        m_state = Error;
+    DartUtilities::reportProblem(m_originDocument, error, m_scriptUrlString);
+}
+
+void DartApplicationLoader::reportError(Dart_Handle error, const String& url)
+{
+    reportError(Dart_GetError(error), url);
+}
+
+void DartApplicationLoader::reportError(const String& error, const String& url)
+{
+    if (m_state < Running)
+        m_state = Error;
+    m_loadCallback->reportError(error, url);
+}
+
+
+}