Headless: make URLRequestDispatcher aware of navigations

headless/app/headless_shell.cc

Index: headless/app/headless_shell.cc
diff --git a/headless/app/headless_shell.cc b/headless/app/headless_shell.cc
index 942fb9bbad7084131d5f94af51c8bdb28cc6e313..91b17493ba08a155c66c66e25fcb1cd9bfd3a85a 100644
--- a/headless/app/headless_shell.cc
+++ b/headless/app/headless_shell.cc
@@ -13,23 +13,13 @@
 #include "base/files/file_path.h"
 #include "base/json/json_writer.h"
 #include "base/location.h"
-#include "base/memory/ptr_util.h"
-#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/strings/string_number_conversions.h"
+#include "headless/app/headless_shell.h"
 #include "headless/app/headless_shell_switches.h"
-#include "headless/public/devtools/domains/emulation.h"
-#include "headless/public/devtools/domains/inspector.h"
-#include "headless/public/devtools/domains/page.h"
-#include "headless/public/devtools/domains/runtime.h"
-#include "headless/public/headless_browser.h"
-#include "headless/public/headless_devtools_client.h"
 #include "headless/public/headless_devtools_target.h"
-#include "headless/public/headless_web_contents.h"
-#include "headless/public/util/deterministic_dispatcher.h"
 #include "headless/public/util/deterministic_http_protocol_handler.h"
-#include "net/base/file_stream.h"
 #include "net/base/io_buffer.h"
 #include "net/base/ip_address.h"
 #include "net/base/net_errors.h"
@@ -54,351 +44,351 @@ bool ParseWindowSize(std::string window_size, gfx::Size* parsed_window_size) {
 }
 }  // namespace
 
-// An application which implements a simple headless browser.
-class HeadlessShell : public HeadlessWebContents::Observer,
-                      emulation::ExperimentalObserver,
-                      inspector::ExperimentalObserver,
-                      page::Observer {
- public:
-  HeadlessShell()
-      : browser_(nullptr),
-        devtools_client_(HeadlessDevToolsClient::Create()),
-        web_contents_(nullptr),
-        processed_page_ready_(false),
-        browser_context_(nullptr),
-        weak_factory_(this) {}
-  ~HeadlessShell() override {}
-
-  void OnStart(HeadlessBrowser* browser) {
-    browser_ = browser;
-
-    HeadlessBrowserContext::Builder context_builder =
-        browser_->CreateBrowserContextBuilder();
-    // TODO(eseckler): These switches should also affect BrowserContexts that
-    // are created via DevTools later.
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kDeterministicFetch)) {
-      deterministic_dispatcher_.reset(
-          new DeterministicDispatcher(browser_->BrowserIOThread()));
-
-      ProtocolHandlerMap protocol_handlers;
-      protocol_handlers[url::kHttpScheme] =
-          base::MakeUnique<DeterministicHttpProtocolHandler>(
-              deterministic_dispatcher_.get(), browser->BrowserIOThread());
-      protocol_handlers[url::kHttpsScheme] =
-          base::MakeUnique<DeterministicHttpProtocolHandler>(
-              deterministic_dispatcher_.get(), browser->BrowserIOThread());
-
-      context_builder.SetProtocolHandlers(std::move(protocol_handlers));
-    }
-    browser_context_ = context_builder.Build();
-    browser_->SetDefaultBrowserContext(browser_context_);
-
-    HeadlessWebContents::Builder builder(
-        browser_context_->CreateWebContentsBuilder());
-    base::CommandLine::StringVector args =
-        base::CommandLine::ForCurrentProcess()->GetArgs();
-
-    // TODO(alexclarke): Should we navigate to about:blank first if using
-    // virtual time?
-    if (args.empty())
-      args.push_back("about:blank");
-    for (auto it = args.rbegin(); it != args.rend(); ++it) {
-      GURL url(*it);
-      HeadlessWebContents* web_contents = builder.SetInitialURL(url).Build();
-      if (!web_contents) {
-        LOG(ERROR) << "Navigation to " << url << " failed";
-        browser_->Shutdown();
-        return;
-      }
-      if (!web_contents_ && !RemoteDebuggingEnabled()) {
-        // TODO(jzfeng): Support observing multiple targets.
-        url_ = url;
-        web_contents_ = web_contents;
-        web_contents_->AddObserver(this);
-      }
-    }
-  }
-
-  void Shutdown() {
-    if (!web_contents_)
+HeadlessShell::HeadlessShell()
+    : browser_(nullptr),
+      devtools_client_(HeadlessDevToolsClient::Create()),
+      web_contents_(nullptr),
+      processed_page_ready_(false),
+      browser_context_(nullptr),
+      weak_factory_(this) {}
+
+HeadlessShell::~HeadlessShell() {}
+
+void HeadlessShell::OnStart(HeadlessBrowser* browser) {
+  browser_ = browser;
+
+  HeadlessBrowserContext::Builder context_builder =
+      browser_->CreateBrowserContextBuilder();
+  // TODO(eseckler): These switches should also affect BrowserContexts that
+  // are created via DevTools later.
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDeterministicFetch)) {
+    deterministic_dispatcher_.reset(
+        new DeterministicDispatcher(browser_->BrowserIOThread()));
+
+    ProtocolHandlerMap protocol_handlers;
+    protocol_handlers[url::kHttpScheme] =
+        base::MakeUnique<DeterministicHttpProtocolHandler>(
+            deterministic_dispatcher_.get(), browser->BrowserIOThread());
+    protocol_handlers[url::kHttpsScheme] =
+        base::MakeUnique<DeterministicHttpProtocolHandler>(
+            deterministic_dispatcher_.get(), browser->BrowserIOThread());
+
+    context_builder.SetProtocolHandlers(std::move(protocol_handlers));
+  }
+  browser_context_ = context_builder.Build();
+  browser_->SetDefaultBrowserContext(browser_context_);
+
+  HeadlessWebContents::Builder builder(
+      browser_context_->CreateWebContentsBuilder());
+  base::CommandLine::StringVector args =
+      base::CommandLine::ForCurrentProcess()->GetArgs();
+
+  // TODO(alexclarke): Should we navigate to about:blank first if using
+  // virtual time?
+  if (args.empty())
+    args.push_back("about:blank");
+  for (auto it = args.rbegin(); it != args.rend(); ++it) {
+    GURL url(*it);
+    HeadlessWebContents* web_contents = builder.SetInitialURL(url).Build();
+    if (!web_contents) {
+      LOG(ERROR) << "Navigation to " << url << " failed";
+      browser_->Shutdown();
       return;
-    if (!RemoteDebuggingEnabled()) {
-      devtools_client_->GetEmulation()->GetExperimental()->RemoveObserver(this);
-      devtools_client_->GetInspector()->GetExperimental()->RemoveObserver(this);
-      devtools_client_->GetPage()->RemoveObserver(this);
-      if (web_contents_->GetDevToolsTarget()) {
-        web_contents_->GetDevToolsTarget()->DetachClient(
-            devtools_client_.get());
-      }
     }
-    web_contents_->RemoveObserver(this);
-    web_contents_ = nullptr;
-    browser_context_->Close();
-    browser_->Shutdown();
-  }
-
-  // HeadlessWebContents::Observer implementation:
-  void DevToolsTargetReady() override {
-    web_contents_->GetDevToolsTarget()->AttachClient(devtools_client_.get());
-    devtools_client_->GetInspector()->GetExperimental()->AddObserver(this);
-    devtools_client_->GetPage()->AddObserver(this);
-    devtools_client_->GetPage()->Enable();
-    // Check if the document had already finished loading by the time we
-    // attached.
-
-    devtools_client_->GetEmulation()->GetExperimental()->AddObserver(this);
-
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kVirtualTimeBudget)) {
-      std::string budget_ms_ascii =
-          base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
-              switches::kVirtualTimeBudget);
-      int budget_ms;
-      CHECK(base::StringToInt(budget_ms_ascii, &budget_ms))
-          << "Expected an integer value for --virtual-time-budget=";
-      devtools_client_->GetEmulation()->GetExperimental()->SetVirtualTimePolicy(
-          emulation::SetVirtualTimePolicyParams::Builder()
-              .SetPolicy(emulation::VirtualTimePolicy::
-                             PAUSE_IF_NETWORK_FETCHES_PENDING)
-              .SetBudget(budget_ms)
-              .Build());
-    } else {
-      PollReadyState();
-    }
-
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kTimeout)) {
-      std::string timeout_ms_ascii =
-          base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
-              switches::kTimeout);
-      int timeout_ms;
-      CHECK(base::StringToInt(timeout_ms_ascii, &timeout_ms))
-          << "Expected an integer value for --timeout=";
-      browser_->BrowserMainThread()->PostDelayedTask(
-          FROM_HERE,
-          base::Bind(&HeadlessShell::FetchTimeout, weak_factory_.GetWeakPtr()),
-          base::TimeDelta::FromMilliseconds(timeout_ms));
+    if (!web_contents_ && !RemoteDebuggingEnabled()) {
+      // TODO(jzfeng): Support observing multiple targets.
+      url_ = url;
+      web_contents_ = web_contents;
+      web_contents_->AddObserver(this);
     }
-
-    // TODO(skyostil): Implement more features to demonstrate the devtools API.
-  }
-
-  void FetchTimeout() {
-    LOG(INFO) << "Timeout.";
-    devtools_client_->GetPage()->GetExperimental()->StopLoading(
-        page::StopLoadingParams::Builder().Build());
   }
+}
 
-  void OnTargetCrashed(const inspector::TargetCrashedParams& params) override {
-    LOG(ERROR) << "Abnormal renderer termination.";
-    // NB this never gets called if remote debugging is enabled.
-    Shutdown();
+void HeadlessShell::Shutdown() {
+  if (!web_contents_)
+    return;
+  if (!RemoteDebuggingEnabled()) {
+    devtools_client_->GetEmulation()->GetExperimental()->RemoveObserver(this);
+    devtools_client_->GetInspector()->GetExperimental()->RemoveObserver(this);
+    devtools_client_->GetPage()->GetExperimental()->RemoveObserver(this);
+    if (web_contents_->GetDevToolsTarget()) {
+      web_contents_->GetDevToolsTarget()->DetachClient(devtools_client_.get());
+    }
   }
+  web_contents_->RemoveObserver(this);
+  web_contents_ = nullptr;
+  browser_context_->Close();
+  browser_->Shutdown();
+}
 
-  void PollReadyState() {
-    // We need to check the current location in addition to the ready state to
-    // be sure the expected page is ready.
-    devtools_client_->GetRuntime()->Evaluate(
-        "document.readyState + ' ' + document.location.href",
-        base::Bind(&HeadlessShell::OnReadyState, weak_factory_.GetWeakPtr()));
-  }
+void HeadlessShell::DevToolsTargetReady() {
+  web_contents_->GetDevToolsTarget()->AttachClient(devtools_client_.get());
+  devtools_client_->GetInspector()->GetExperimental()->AddObserver(this);
+  devtools_client_->GetPage()->GetExperimental()->AddObserver(this);
+  devtools_client_->GetPage()->Enable();
+  // Check if the document had already finished loading by the time we
+  // attached.
+
+  devtools_client_->GetEmulation()->GetExperimental()->AddObserver(this);
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDeterministicFetch)) {
+    devtools_client_->GetPage()->GetExperimental()->SetControlNavigations(
+        headless::page::SetControlNavigationsParams::Builder()
+            .SetEnabled(true)
+            .Build());
+  }
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kVirtualTimeBudget)) {
+    std::string budget_ms_ascii =
+        base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+            switches::kVirtualTimeBudget);
+    int budget_ms;
+    CHECK(base::StringToInt(budget_ms_ascii, &budget_ms))
+        << "Expected an integer value for --virtual-time-budget=";
+    devtools_client_->GetEmulation()->GetExperimental()->SetVirtualTimePolicy(
+        emulation::SetVirtualTimePolicyParams::Builder()
+            .SetPolicy(
+                emulation::VirtualTimePolicy::PAUSE_IF_NETWORK_FETCHES_PENDING)
+            .SetBudget(budget_ms)
+            .Build());
+  } else {
+    PollReadyState();
+  }
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kTimeout)) {
+    std::string timeout_ms_ascii =
+        base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+            switches::kTimeout);
+    int timeout_ms;
+    CHECK(base::StringToInt(timeout_ms_ascii, &timeout_ms))
+        << "Expected an integer value for --timeout=";
+    browser_->BrowserMainThread()->PostDelayedTask(
+        FROM_HERE,
+        base::Bind(&HeadlessShell::FetchTimeout, weak_factory_.GetWeakPtr()),
+        base::TimeDelta::FromMilliseconds(timeout_ms));
+  }
+
+  // TODO(skyostil): Implement more features to demonstrate the devtools API.
+}
 
-  void OnReadyState(std::unique_ptr<runtime::EvaluateResult> result) {
-    std::string ready_state_and_url;
-    if (result->GetResult()->GetValue()->GetAsString(&ready_state_and_url)) {
-      std::stringstream stream(ready_state_and_url);
-      std::string ready_state;
-      std::string url;
-      stream >> ready_state;
-      stream >> url;
+void HeadlessShell::FetchTimeout() {
+  LOG(INFO) << "Timeout.";
+  devtools_client_->GetPage()->GetExperimental()->StopLoading(
+      page::StopLoadingParams::Builder().Build());
+}
 
-      if (ready_state == "complete" &&
-          (url_.spec() == url || url != "about:blank")) {
-        OnPageReady();
-        return;
-      }
-    }
-  }
+void HeadlessShell::OnTargetCrashed(
+    const inspector::TargetCrashedParams& params) {
+  LOG(ERROR) << "Abnormal renderer termination.";
+  // NB this never gets called if remote debugging is enabled.
+  Shutdown();
+}
 
-  // emulation::Observer implementation:
-  void OnVirtualTimeBudgetExpired(
-      const emulation::VirtualTimeBudgetExpiredParams& params) override {
-    OnPageReady();
-  }
+void HeadlessShell::PollReadyState() {
+  // We need to check the current location in addition to the ready state to
+  // be sure the expected page is ready.
+  devtools_client_->GetRuntime()->Evaluate(
+      "document.readyState + ' ' + document.location.href",
+      base::Bind(&HeadlessShell::OnReadyState, weak_factory_.GetWeakPtr()));
+}
 
-  // page::Observer implementation:
-  void OnLoadEventFired(const page::LoadEventFiredParams& params) override {
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kVirtualTimeBudget)) {
+void HeadlessShell::OnReadyState(
+    std::unique_ptr<runtime::EvaluateResult> result) {
+  std::string ready_state_and_url;
+  if (result->GetResult()->GetValue()->GetAsString(&ready_state_and_url)) {
+    std::stringstream stream(ready_state_and_url);
+    std::string ready_state;
+    std::string url;
+    stream >> ready_state;
+    stream >> url;
+
+    if (ready_state == "complete" &&
+        (url_.spec() == url || url != "about:blank")) {
+      OnPageReady();
       return;
     }
-    OnPageReady();
   }
+}
 
-  void OnPageReady() {
-    if (processed_page_ready_)
-      return;
-    processed_page_ready_ = true;
-
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kDumpDom)) {
-      FetchDom();
-    } else if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-                   switches::kRepl)) {
-      LOG(INFO)
-          << "Type a Javascript expression to evaluate or \"quit\" to exit.";
-      InputExpression();
-    } else if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-                   switches::kScreenshot)) {
-      CaptureScreenshot();
-    } else {
-      Shutdown();
-    }
-  }
+// emulation::Observer implementation:
+void HeadlessShell::OnVirtualTimeBudgetExpired(
+    const emulation::VirtualTimeBudgetExpiredParams& params) {
+  OnPageReady();
+}
 
-  void FetchDom() {
-    devtools_client_->GetRuntime()->Evaluate(
-        "document.body.innerHTML",
-        base::Bind(&HeadlessShell::OnDomFetched, weak_factory_.GetWeakPtr()));
-  }
-
-  void OnDomFetched(std::unique_ptr<runtime::EvaluateResult> result) {
-    if (result->HasExceptionDetails()) {
-      LOG(ERROR) << "Failed to evaluate document.body.innerHTML: "
-                 << result->GetExceptionDetails()->GetText();
-    } else {
-      std::string dom;
-      if (result->GetResult()->GetValue()->GetAsString(&dom)) {
-        printf("%s\n", dom.c_str());
-      }
-    }
-    Shutdown();
+// page::Observer implementation:
+void HeadlessShell::OnLoadEventFired(const page::LoadEventFiredParams& params) {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kVirtualTimeBudget)) {
+    return;
   }
+  OnPageReady();
+}
 
-  void InputExpression() {
-    // Note that a real system should read user input asynchronously, because
-    // otherwise all other browser activity is suspended (e.g., page loading).
-    printf(">>> ");
-    std::stringstream expression;
-    while (true) {
-      int c = fgetc(stdin);
-      if (c == EOF || c == '\n') {
-        break;
-      }
-      expression << static_cast<char>(c);
-    }
-    if (expression.str() == "quit") {
-      Shutdown();
-      return;
-    }
-    devtools_client_->GetRuntime()->Evaluate(
-        expression.str(), base::Bind(&HeadlessShell::OnExpressionResult,
-                                     weak_factory_.GetWeakPtr()));
-  }
+void HeadlessShell::OnNavigationRequested(
+    const headless::page::NavigationRequestedParams& params) {
+  deterministic_dispatcher_->NavigationRequested(
+      base::MakeUnique<ShellNavigationRequest>(weak_factory_.GetWeakPtr(),
+                                               params));
+}
 
-  void OnExpressionResult(std::unique_ptr<runtime::EvaluateResult> result) {
-    std::unique_ptr<base::Value> value = result->Serialize();
-    std::string result_json;
-    base::JSONWriter::Write(*value, &result_json);
-    printf("%s\n", result_json.c_str());
+void HeadlessShell::OnPageReady() {
+  if (processed_page_ready_)
+    return;
+  processed_page_ready_ = true;
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kDumpDom)) {
+    FetchDom();
+  } else if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+                 switches::kRepl)) {
+    LOG(INFO)
+        << "Type a Javascript expression to evaluate or \"quit\" to exit.";
     InputExpression();
+  } else if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+                 switches::kScreenshot)) {
+    CaptureScreenshot();
+  } else {
+    Shutdown();
   }
+}
 
-  void CaptureScreenshot() {
-    devtools_client_->GetPage()->GetExperimental()->CaptureScreenshot(
-        page::CaptureScreenshotParams::Builder().Build(),
-        base::Bind(&HeadlessShell::OnScreenshotCaptured,
-                   weak_factory_.GetWeakPtr()));
-  }
+void HeadlessShell::FetchDom() {
+  devtools_client_->GetRuntime()->Evaluate(
+      "document.body.innerHTML",
+      base::Bind(&HeadlessShell::OnDomFetched, weak_factory_.GetWeakPtr()));
+}
 
-  void OnScreenshotCaptured(
-      std::unique_ptr<page::CaptureScreenshotResult> result) {
-    base::FilePath file_name =
-        base::CommandLine::ForCurrentProcess()->GetSwitchValuePath(
-            switches::kScreenshot);
-    if (file_name.empty()) {
-      file_name = base::FilePath().AppendASCII(kDefaultScreenshotFileName);
+void HeadlessShell::OnDomFetched(
+    std::unique_ptr<runtime::EvaluateResult> result) {
+  if (result->HasExceptionDetails()) {
+    LOG(ERROR) << "Failed to evaluate document.body.innerHTML: "
+               << result->GetExceptionDetails()->GetText();
+  } else {
+    std::string dom;
+    if (result->GetResult()->GetValue()->GetAsString(&dom)) {
+      printf("%s\n", dom.c_str());
     }
+  }
+  Shutdown();
+}
 
-    screenshot_file_stream_.reset(
-        new net::FileStream(browser_->BrowserFileThread()));
-    const int open_result = screenshot_file_stream_->Open(
-        file_name, base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE |
-                       base::File::FLAG_ASYNC,
-        base::Bind(&HeadlessShell::OnScreenshotFileOpened,
-                   weak_factory_.GetWeakPtr(), base::Passed(std::move(result)),
-                   file_name));
-    if (open_result != net::ERR_IO_PENDING) {
-      // Operation could not be started.
-      OnScreenshotFileOpened(nullptr, file_name, open_result);
+void HeadlessShell::InputExpression() {
+  // Note that a real system should read user input asynchronously, because
+  // otherwise all other browser activity is suspended (e.g., page loading).
+  printf(">>> ");
+  std::stringstream expression;
+  while (true) {
+    int c = fgetc(stdin);
+    if (c == EOF || c == '\n') {
+      break;
     }
+    expression << static_cast<char>(c);
+  }
+  if (expression.str() == "quit") {
+    Shutdown();
+    return;
   }
+  devtools_client_->GetRuntime()->Evaluate(
+      expression.str(), base::Bind(&HeadlessShell::OnExpressionResult,
+                                   weak_factory_.GetWeakPtr()));
+}
 
-  void OnScreenshotFileOpened(
-      std::unique_ptr<page::CaptureScreenshotResult> result,
-      const base::FilePath file_name,
-      const int open_result) {
-    if (open_result != net::OK) {
-      LOG(ERROR) << "Writing screenshot to file " << file_name.value()
-                 << " was unsuccessful, could not open file: "
-                 << net::ErrorToString(open_result);
-      return;
-    }
+void HeadlessShell::OnExpressionResult(
+    std::unique_ptr<runtime::EvaluateResult> result) {
+  std::unique_ptr<base::Value> value = result->Serialize();
+  std::string result_json;
+  base::JSONWriter::Write(*value, &result_json);
+  printf("%s\n", result_json.c_str());
+  InputExpression();
+}
 
-    std::string decoded_png;
-    base::Base64Decode(result->GetData(), &decoded_png);
-    scoped_refptr<net::IOBufferWithSize> buf =
-        new net::IOBufferWithSize(decoded_png.size());
-    memcpy(buf->data(), decoded_png.data(), decoded_png.size());
-    const int write_result = screenshot_file_stream_->Write(
-        buf.get(), buf->size(),
-        base::Bind(&HeadlessShell::OnScreenshotFileWritten,
-                   weak_factory_.GetWeakPtr(), file_name, buf->size()));
-    if (write_result != net::ERR_IO_PENDING) {
-      // Operation may have completed successfully or failed.
-      OnScreenshotFileWritten(file_name, buf->size(), write_result);
-    }
-  }
+void HeadlessShell::CaptureScreenshot() {
+  devtools_client_->GetPage()->GetExperimental()->CaptureScreenshot(
+      page::CaptureScreenshotParams::Builder().Build(),
+      base::Bind(&HeadlessShell::OnScreenshotCaptured,
+                 weak_factory_.GetWeakPtr()));
+}
 
-  void OnScreenshotFileWritten(const base::FilePath file_name,
-                               const int length,
-                               const int write_result) {
-    if (write_result < length) {
-      // TODO(eseckler): Support recovering from partial writes.
-      LOG(ERROR) << "Writing screenshot to file " << file_name.value()
-                 << " was unsuccessful: " << net::ErrorToString(write_result);
-    } else {
-      LOG(INFO) << "Screenshot written to file " << file_name.value() << "."
-                << std::endl;
-    }
-    int close_result = screenshot_file_stream_->Close(base::Bind(
-        &HeadlessShell::OnScreenshotFileClosed, weak_factory_.GetWeakPtr()));
-    if (close_result != net::ERR_IO_PENDING) {
-      // Operation could not be started.
-      OnScreenshotFileClosed(close_result);
-    }
+void HeadlessShell::OnScreenshotCaptured(
+    std::unique_ptr<page::CaptureScreenshotResult> result) {
+  base::FilePath file_name =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValuePath(
+          switches::kScreenshot);
+  if (file_name.empty()) {
+    file_name = base::FilePath().AppendASCII(kDefaultScreenshotFileName);
+  }
+
+  screenshot_file_stream_.reset(
+      new net::FileStream(browser_->BrowserFileThread()));
+  const int open_result = screenshot_file_stream_->Open(
+      file_name, base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE |
+                     base::File::FLAG_ASYNC,
+      base::Bind(&HeadlessShell::OnScreenshotFileOpened,
+                 weak_factory_.GetWeakPtr(), base::Passed(std::move(result)),
+                 file_name));
+  if (open_result != net::ERR_IO_PENDING) {
+    // Operation could not be started.
+    OnScreenshotFileOpened(nullptr, file_name, open_result);
   }
+}
 
-  void OnScreenshotFileClosed(const int close_result) { Shutdown(); }
+void HeadlessShell::OnScreenshotFileOpened(
+    std::unique_ptr<page::CaptureScreenshotResult> result,
+    const base::FilePath file_name,
+    const int open_result) {
+  if (open_result != net::OK) {
+    LOG(ERROR) << "Writing screenshot to file " << file_name.value()
+               << " was unsuccessful, could not open file: "
+               << net::ErrorToString(open_result);
+    return;
+  }
+
+  std::string decoded_png;
+  base::Base64Decode(result->GetData(), &decoded_png);
+  scoped_refptr<net::IOBufferWithSize> buf =
+      new net::IOBufferWithSize(decoded_png.size());
+  memcpy(buf->data(), decoded_png.data(), decoded_png.size());
+  const int write_result = screenshot_file_stream_->Write(
+      buf.get(), buf->size(),
+      base::Bind(&HeadlessShell::OnScreenshotFileWritten,
+                 weak_factory_.GetWeakPtr(), file_name, buf->size()));
+  if (write_result != net::ERR_IO_PENDING) {
+    // Operation may have completed successfully or failed.
+    OnScreenshotFileWritten(file_name, buf->size(), write_result);
+  }
+}
 
-  bool RemoteDebuggingEnabled() const {
-    const base::CommandLine& command_line =
-        *base::CommandLine::ForCurrentProcess();
-    return command_line.HasSwitch(switches::kRemoteDebuggingPort);
+void HeadlessShell::OnScreenshotFileWritten(const base::FilePath file_name,
+                                            const int length,
+                                            const int write_result) {
+  if (write_result < length) {
+    // TODO(eseckler): Support recovering from partial writes.
+    LOG(ERROR) << "Writing screenshot to file " << file_name.value()
+               << " was unsuccessful: " << net::ErrorToString(write_result);
+  } else {
+    LOG(INFO) << "Screenshot written to file " << file_name.value() << "."
+              << std::endl;
+  }
+  int close_result = screenshot_file_stream_->Close(base::Bind(
+      &HeadlessShell::OnScreenshotFileClosed, weak_factory_.GetWeakPtr()));
+  if (close_result != net::ERR_IO_PENDING) {
+    // Operation could not be started.
+    OnScreenshotFileClosed(close_result);
   }
+}
 
- private:
-  GURL url_;
-  HeadlessBrowser* browser_;  // Not owned.
-  std::unique_ptr<HeadlessDevToolsClient> devtools_client_;
-  HeadlessWebContents* web_contents_;
-  bool processed_page_ready_;
-  std::unique_ptr<net::FileStream> screenshot_file_stream_;
-  HeadlessBrowserContext* browser_context_;
-  std::unique_ptr<DeterministicDispatcher> deterministic_dispatcher_;
-  base::WeakPtrFactory<HeadlessShell> weak_factory_;
+void HeadlessShell::OnScreenshotFileClosed(const int close_result) {
+  Shutdown();
+}
 
-  DISALLOW_COPY_AND_ASSIGN(HeadlessShell);
-};
+bool HeadlessShell::RemoteDebuggingEnabled() const {
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+  return command_line.HasSwitch(switches::kRemoteDebuggingPort);
+}
 
 bool ValidateCommandLine(const base::CommandLine& command_line) {
   if (!command_line.HasSwitch(switches::kRemoteDebuggingPort)) {