Introduce background Download process to android

This change adds a new download process to android.
This process will handle download in the background and may outlive chrome
Unlike other ChildProcessService, DownloadProcessService is a started service as it manage its own lifecycle:
When a download started, the download service will start running
When all download finishes, the Download service will be stopped

BUG=545640

Review URL: https://codereview.chromium.org/1622743005

Cr-Commit-Position: refs/heads/master@{#373608}

chrome/android/java/AndroidManifest.xml

@@ -643,6 +643,17 @@ android:value="true" />
             android:exported="false" />
         {% endfor %}
 
+        <!-- Background download process, it may outlive chrome if download does not finish
+             when user kills chrome. Once created, the process will manage its own lifecycle.
+             To work around an issue in earlier android versions that a bound service will
+             get killed when chrome goes away, this service will only communicate with the
+             browser process through callbacks. -->
+        <service android:name="org.chromium.content.app.DownloadProcessService"
+            android:process=":download"
+            android:permission="{{ manifest_package }}.permission.CHILD_SERVICE"
+            android:isolatedProcess="false"
+            android:exported="false"/>
+
         <receiver android:name="org.chromium.chrome.browser.download.DownloadBroadcastReceiver"
             android:exported="false">
             <intent-filter>

content/app/BUILD.gn

@@ -12,6 +12,7 @@ content_app_sources = [
   "android/content_jni_onload.cc",
   "android/content_main.cc",
   "android/content_main.h",
+  "android/download_main.cc",
   "android/library_loader_hooks.cc",
   "android/library_loader_hooks.h",
   "content_main.cc",

content/app/android/download_main.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/message_loop/message_loop.h"
+#include "base/threading/platform_thread.h"
+#include "content/public/common/main_function_params.h"
+
+namespace content {
+
+// Mainline routine for running as the download process.
+int DownloadMain(const MainFunctionParams& parameters) {
+  // The main message loop of the utility process.
+  base::MessageLoop main_message_loop;
+  base::PlatformThread::SetName("CrDownloadMain");
+  base::MessageLoop::current()->Run();
+
+  return 0;
+}
+
+}  // namespace content

content/app/content_main_runner.cc

@@ -121,6 +121,9 @@ extern int PpapiBrokerMain(const MainFunctionParams&);
 #endif
 extern int RendererMain(const content::MainFunctionParams&);
 extern int UtilityMain(const MainFunctionParams&);
+#if defined(OS_ANDROID)
+extern int DownloadMain(const MainFunctionParams&);
+#endif
 }  // namespace content
 
 namespace content {
@@ -343,6 +346,9 @@ int RunNamedProcessTypeMain(
     { switches::kUtilityProcess,     UtilityMain },
     { switches::kRendererProcess,    RendererMain },
     { switches::kGpuProcess,         GpuMain },
+#if defined(OS_ANDROID)
+    { switches::kDownloadProcess,    DownloadMain},
+#endif
 #endif  // !CHROME_MULTIPLE_DLL_BROWSER
   };
 

content/browser/android/child_process_launcher_android.cc

@@ -13,12 +13,16 @@
 #include "base/android/jni_array.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "content/browser/file_descriptor_info_impl.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
 #include "content/browser/media/android/browser_media_player_manager.h"
 #include "content/browser/media/android/media_web_contents_observer_android.h"
 #include "content/browser/web_contents/web_contents_impl.h"
+#include "content/common/child_process_host_impl.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/render_process_host.h"
+#include "content/public/common/content_client.h"
 #include "content/public/common/content_switches.h"
 #include "jni/ChildProcessLauncher_jni.h"
 #include "media/base/android/media_player_android.h"
@@ -84,6 +88,21 @@ static void SetSurfacePeer(
   }
 }
 
+void LaunchDownloadProcess(base::CommandLine* cmd_line) {
+  scoped_ptr<base::CommandLine> cmd_line_deleter(cmd_line);
+
+  JNIEnv* env = AttachCurrentThread();
+  DCHECK(env);
+
+  // Create the Command line String[]
+  ScopedJavaLocalRef<jobjectArray> j_argv =
+      ToJavaArrayOfStrings(env, cmd_line->argv());
+
+  // TODO(qinmin): pass download parameters here.
+  Java_ChildProcessLauncher_startDownloadProcessIfNecessary(
+      env, base::android::GetApplicationContext(), j_argv.obj());
+}
+
 }  // anonymous namespace
 
 // Called from ChildProcessLauncher.java when the ChildProcess was
@@ -103,6 +122,32 @@ static void OnChildProcessStarted(JNIEnv*,
   delete callback;
 }
 
+void StartDownloadProcessIfNecessary() {
+  base::FilePath exe_path = content::ChildProcessHost::GetChildPath(
+      content::ChildProcessHost::CHILD_NORMAL);
+  if (exe_path.empty()) {
+    NOTREACHED() << "Unable to get download process binary name.";
+    return;
+  }
+  base::CommandLine* cmd_line = new base::CommandLine(exe_path);
+  cmd_line->AppendSwitchASCII(switches::kProcessType,
+                              switches::kDownloadProcess);
+  cmd_line->AppendSwitch(switches::kNoSandbox);
+
+  const base::CommandLine browser_command_line =
+      *base::CommandLine::ForCurrentProcess();
+  static const char* kForwardSwitches[] = {
+      switches::kDisableLogging,
+      switches::kEnableLogging,
+      switches::kLoggingLevel,
+  };
+  cmd_line->CopySwitchesFrom(browser_command_line, kForwardSwitches,
+                             arraysize(kForwardSwitches));
+  CHECK(!cmd_line->HasSwitch(switches::kSingleProcess));
+  BrowserThread::PostTask(BrowserThread::PROCESS_LAUNCHER, FROM_HERE,
+                          base::Bind(&LaunchDownloadProcess, cmd_line));
+}
+
 void StartChildProcess(
     const base::CommandLine::StringVector& argv,
     int child_process_id,

content/browser/android/child_process_launcher_android.h

@@ -29,6 +29,10 @@ void StartChildProcess(
     const std::map<int, base::MemoryMappedFile::Region>& regions,
     const StartChildProcessCallback& callback);
 
+// Starts the background download process if it hasn't been started.
+// TODO(qinmin): pass the download parameters here and pass it to java side.
+void StartDownloadProcessIfNecessary();
+
 // Stops a child process based on the handle returned form
 // StartChildProcess.
 void StopChildProcess(base::ProcessHandle handle);

content/content_app.gypi

@@ -25,6 +25,7 @@
     'app/android/content_jni_onload.cc',
     'app/android/content_main.cc',
     'app/android/content_main.h',
+    'app/android/download_main.cc',
     'app/android/library_loader_hooks.cc',
     'app/android/library_loader_hooks.h',
     'app/content_main.cc',

content/public/android/java/res/values/ids.xml

+<?xml version="1.0" encoding="utf-8"?>
+
+<!-- Copyright 2016 The Chromium Authors. All rights reserved.
+
+     Use of this source code is governed by a BSD-style license that can be
+     found in the LICENSE file.
+-->
+
+<resources>
+    <!-- Download service notification -->
+    <item type="id" name="download_service_notification" />
+</resources>

content/public/android/java/src/org/chromium/content/app/ChildProcessService.java

@@ -27,8 +27,8 @@ import org.chromium.base.library_loader.LibraryProcessType;
 import org.chromium.base.library_loader.Linker;
 import org.chromium.base.library_loader.ProcessInitException;
 import org.chromium.content.browser.ChildProcessConstants;
-import org.chromium.content.browser.ChildProcessLauncher;
 import org.chromium.content.browser.FileDescriptorInfo;
+import org.chromium.content.common.ContentSwitches;
 import org.chromium.content.common.IChildProcessCallback;
 import org.chromium.content.common.IChildProcessService;
 import org.chromium.content.common.SurfaceWrapper;
@@ -51,6 +51,7 @@ import java.util.concurrent.atomic.AtomicReference;
 public class ChildProcessService extends Service {
     private static final String MAIN_THREAD_NAME = "ChildProcessMain";
     private static final String TAG = "ChildProcessService";
+    protected static final FileDescriptorInfo[] EMPTY_FILE_DESCRIPTOR_INFO = {};
     private IChildProcessCallback mCallback;
 
     // This is the native "Main" thread for the renderer / utility process.
@@ -289,10 +290,10 @@ public class ChildProcessService extends Service {
                 mFdInfos = new FileDescriptorInfo[fdInfosAsParcelable.length];
                 System.arraycopy(fdInfosAsParcelable, 0, mFdInfos, 0, fdInfosAsParcelable.length);
             } else {
-                // TODO(qinmin): On earlier androird versions, a started service running in another
-                // process can get killed after Chrome is killed. To work around this issue, client
-                // will never bind to the service. As a result, the file descriptors needs to be
-                // passed through an intent when starting the service.
+                String processType = ContentSwitches.getSwitchValue(
+                        mCommandLineParams, ContentSwitches.SWITCH_PROCESS_TYPE);
+                assert ContentSwitches.SWITCH_DOWNLOAD_PROCESS.equals(processType);
+                mFdInfos = EMPTY_FILE_DESCRIPTOR_INFO;
             }
             Bundle sharedRelros = bundle.getBundle(Linker.EXTRA_LINKER_SHARED_RELROS);
             if (sharedRelros != null) {

content/public/android/java/src/org/chromium/content/app/DownloadProcessService.java

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.content.app;
+
+import android.annotation.SuppressLint;
+import android.app.Notification;
+import android.content.Intent;
+import android.os.Build;
+import android.os.Bundle;
+import android.os.IBinder;
+import android.os.RemoteException;
+
+import org.chromium.base.Log;
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.content.R;
+import org.chromium.content.browser.ChildProcessConstants;
+import org.chromium.content.common.IChildProcessCallback;
+
+/**
+ * Background download process for handling all transferable downloads.
+ */
+@JNINamespace("content")
+public class DownloadProcessService extends ChildProcessService {
+    private static final String TAG = "DownloadProcess";
+    private long mClientContext;
+    private IChildProcessCallback mCallback;
+    private int mDownloadCount;
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        // TODO(qinmin): Use the first pending download as notification, or
+        // get a more proper notification for this.
+        startForeground(R.id.download_service_notification, new Notification());
+    }
+
+    @Override
+    @SuppressLint("NewApi")
+    public int onStartCommand(Intent intent, int flags, int startId) {
+        assert Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2;
+        initializeParams(intent);
+        Bundle bundle = intent.getExtras();
+        if (bundle != null) {
+            IBinder binder = bundle.getBinder(ChildProcessConstants.EXTRA_CHILD_PROCESS_CALLBACK);
+            mCallback = IChildProcessCallback.Stub.asInterface(binder);
+            getServiceInfo(bundle);
+        }
+        return START_STICKY;
+    }
+
+    /**
+     * Will be called by the native side when a download starts or is rejected.
+     *
+     * @CalledByNative
+     */
+    private void onDownloadStarted(boolean started, int downloadId) {
+        if (mCallback != null) {
+            try {
+                mCallback.onDownloadStarted(started, downloadId);
+            } catch (RemoteException e) {
+                Log.e(TAG, "Unable to callback the browser process.", e);
+            }
+        }
+        if (started) mDownloadCount++;
+    }
+
+    /**
+     * Will be called by the native side when a download completes.
+     *
+     * @CalledByNative
+     */
+    private void onDownloadCompleted(boolean success) {
+        mDownloadCount--;
+        if (mDownloadCount == 0) stopSelf();
+    }
+}
\ No newline at end of file

content/public/android/java/src/org/chromium/content/browser/ChildProcessConnectionImpl.java

@@ -13,12 +13,10 @@ import android.os.DeadObjectException;
 import android.os.IBinder;
 import android.os.RemoteException;
 
-import org.chromium.base.CpuFeatures;
 import org.chromium.base.Log;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.TraceEvent;
 import org.chromium.base.VisibleForTesting;
-import org.chromium.base.library_loader.Linker;
 import org.chromium.content.app.ChildProcessService;
 import org.chromium.content.app.ChromiumLinkerParams;
 import org.chromium.content.common.IChildProcessCallback;
@@ -331,16 +329,9 @@ public class ChildProcessConnectionImpl implements ChildProcessConnection {
             assert mServiceConnectComplete && mService != null;
             assert mConnectionParams != null;
 
-            Bundle bundle = new Bundle();
-            bundle.putStringArray(
-                    ChildProcessConstants.EXTRA_COMMAND_LINE, mConnectionParams.mCommandLine);
-            bundle.putParcelableArray(
-                    ChildProcessConstants.EXTRA_FILES, mConnectionParams.mFilesToBeMapped);
-            // Add the CPU properties now.
-            bundle.putInt(ChildProcessConstants.EXTRA_CPU_COUNT, CpuFeatures.getCount());
-            bundle.putLong(ChildProcessConstants.EXTRA_CPU_FEATURES, CpuFeatures.getMask());
-            bundle.putBundle(Linker.EXTRA_LINKER_SHARED_RELROS,
-                             mConnectionParams.mSharedRelros);
+            Bundle bundle =
+                    ChildProcessLauncher.createsServiceBundle(mConnectionParams.mCommandLine,
+                            mConnectionParams.mFilesToBeMapped, mConnectionParams.mSharedRelros);
             try {
                 mPid = mService.setupConnection(bundle, mConnectionParams.mCallback);
                 assert mPid != 0 : "Child service claims to be run by a process of pid=0.";

content/public/android/java/src/org/chromium/content/browser/ChildProcessConstants.java

@@ -19,4 +19,11 @@ public class ChildProcessConstants {
     // Used to pass the CPU features mask to child processes.
     public static final String EXTRA_CPU_FEATURES =
             "com.google.android.apps.chrome.extra.cpu_features";
+
+    // Used to pass the IChildProcessCallback to a child process. For a started service,
+    // file descriptors cannot be passed in the intent that starts the service. As a result,
+    // a Binder object needs to be passed through which the child process can retrieve the file
+    // descriptors.
+    public static final String EXTRA_CHILD_PROCESS_CALLBACK =
+            "com.google.android.apps.chrome.extra.child_process_callback";
 }

content/public/android/java/src/org/chromium/content/browser/ChildProcessLauncher.java

@@ -4,10 +4,14 @@
 
 package org.chromium.content.browser;
 
+import android.annotation.SuppressLint;
 import android.content.Context;
+import android.content.Intent;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManager;
 import android.graphics.SurfaceTexture;
+import android.os.Build;
+import android.os.Bundle;
 import android.os.ParcelFileDescriptor;
 import android.os.RemoteException;
 import android.text.TextUtils;
@@ -15,6 +19,7 @@ import android.util.Pair;
 import android.view.Surface;
 
 import org.chromium.base.CommandLine;
+import org.chromium.base.CpuFeatures;
 import org.chromium.base.Log;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.TraceEvent;
@@ -24,8 +29,10 @@ import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.library_loader.Linker;
 import org.chromium.content.app.ChildProcessService;
 import org.chromium.content.app.ChromiumLinkerParams;
+import org.chromium.content.app.DownloadProcessService;
 import org.chromium.content.app.PrivilegedProcessService;
 import org.chromium.content.app.SandboxedProcessService;
+import org.chromium.content.common.ContentSwitches;
 import org.chromium.content.common.IChildProcessCallback;
 import org.chromium.content.common.SurfaceWrapper;
 
@@ -47,11 +54,7 @@ public class ChildProcessLauncher {
     static final int CALLBACK_FOR_GPU_PROCESS = 1;
     static final int CALLBACK_FOR_RENDERER_PROCESS = 2;
     static final int CALLBACK_FOR_UTILITY_PROCESS = 3;
-
-    private static final String SWITCH_PROCESS_TYPE = "type";
-    private static final String SWITCH_RENDERER_PROCESS = "renderer";
-    private static final String SWITCH_UTILITY_PROCESS = "utility";
-    private static final String SWITCH_GPU_PROCESS = "gpu-process";
+    static final int CALLBACK_FOR_DOWNLOAD_PROCESS = 4;
 
     /**
      * Allows specifying the package name for looking up child services
@@ -110,7 +113,7 @@ public class ChildProcessLauncher {
                 mFreeConnectionIndices.add(i);
             }
             mChildClass =
-                inSandbox ? SandboxedProcessService.class : PrivilegedProcessService.class;
+                    inSandbox ? SandboxedProcessService.class : PrivilegedProcessService.class;
             mInSandbox = inSandbox;
         }
 
@@ -567,20 +570,6 @@ public class ChildProcessLauncher {
         }
     }
 
-    private static String getSwitchValue(final String[] commandLine, String switchKey) {
-        if (commandLine == null || switchKey == null) {
-            return null;
-        }
-        // This format should be matched with the one defined in command_line.h.
-        final String switchKeyPrefix = "--" + switchKey + "=";
-        for (String command : commandLine) {
-            if (command != null && command.startsWith(switchKeyPrefix)) {
-                return command.substring(switchKeyPrefix.length());
-            }
-        }
-        return null;
-    }
-
     @CalledByNative
     private static FileDescriptorInfo makeFdInfo(
             int id, int fd, boolean autoClose, long offset, long size) {
@@ -617,13 +606,14 @@ public class ChildProcessLauncher {
 
         int callbackType = CALLBACK_FOR_UNKNOWN_PROCESS;
         boolean inSandbox = true;
-        String processType = getSwitchValue(commandLine, SWITCH_PROCESS_TYPE);
-        if (SWITCH_RENDERER_PROCESS.equals(processType)) {
+        String processType =
+                ContentSwitches.getSwitchValue(commandLine, ContentSwitches.SWITCH_PROCESS_TYPE);
+        if (ContentSwitches.SWITCH_RENDERER_PROCESS.equals(processType)) {
             callbackType = CALLBACK_FOR_RENDERER_PROCESS;
-        } else if (SWITCH_GPU_PROCESS.equals(processType)) {
+        } else if (ContentSwitches.SWITCH_GPU_PROCESS.equals(processType)) {
             callbackType = CALLBACK_FOR_GPU_PROCESS;
             inSandbox = false;
-        } else if (SWITCH_UTILITY_PROCESS.equals(processType)) {
+        } else if (ContentSwitches.SWITCH_UTILITY_PROCESS.equals(processType)) {
             // We only support sandboxed right now.
             callbackType = CALLBACK_FOR_UTILITY_PROCESS;
         } else {
@@ -634,6 +624,39 @@ public class ChildProcessLauncher {
                 callbackType, inSandbox);
     }
 
+    /**
+     * Spawns a background download process if it hasn't been started. The download process will
+     * manage its own lifecyle and can outlive chrome.
+     *
+     * @param context Context used to obtain the application context.
+     * @param commandLine The child process command line argv.
+     */
+    @SuppressLint("NewApi")
+    @CalledByNative
+    private static void startDownloadProcessIfNecessary(
+            Context context, final String[] commandLine) {
+        assert Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2;
+        String processType =
+                ContentSwitches.getSwitchValue(commandLine, ContentSwitches.SWITCH_PROCESS_TYPE);
+        assert ContentSwitches.SWITCH_DOWNLOAD_PROCESS.equals(processType);
+
+        Intent intent = new Intent();
+        intent.setClass(context, DownloadProcessService.class);
+        intent.setPackage(context.getPackageName());
+        intent.putExtra(ChildProcessConstants.EXTRA_COMMAND_LINE, commandLine);
+        Bundle bundle =
+                createsServiceBundle(commandLine, null, Linker.getInstance().getSharedRelros());
+        // Pid doesn't matter for download process.
+        bundle.putBinder(ChildProcessConstants.EXTRA_CHILD_PROCESS_CALLBACK,
+                createCallback(0, CALLBACK_FOR_DOWNLOAD_PROCESS).asBinder());
+        intent.putExtras(bundle);
+        ChromiumLinkerParams linkerParams = getLinkerParamsForNewConnection();
+        if (linkerParams != null) {
+            linkerParams.addIntentExtras(intent);
+        }
+        context.startService(intent);
+    }
+
     private static void startInternal(
             Context context,
             final String[] commandLine,
@@ -675,6 +698,23 @@ public class ChildProcessLauncher {
         }
     }
 
+    /**
+     * Create the common bundle to be passed to child processes.
+     * @param context Application context.
+     * @param commandLine Command line params to be passed to the service.
+     * @param linkerParams Linker params to start the service.
+     */
+    protected static Bundle createsServiceBundle(
+            String[] commandLine, FileDescriptorInfo[] filesToBeMapped, Bundle sharedRelros) {
+        Bundle bundle = new Bundle();
+        bundle.putStringArray(ChildProcessConstants.EXTRA_COMMAND_LINE, commandLine);
+        bundle.putParcelableArray(ChildProcessConstants.EXTRA_FILES, filesToBeMapped);
+        bundle.putInt(ChildProcessConstants.EXTRA_CPU_COUNT, CpuFeatures.getCount());
+        bundle.putLong(ChildProcessConstants.EXTRA_CPU_FEATURES, CpuFeatures.getMask());
+        bundle.putBundle(Linker.EXTRA_LINKER_SHARED_RELROS, sharedRelros);
+        return bundle;
+    }
+
     @VisibleForTesting
     static void triggerConnectionSetup(
             final ChildProcessConnection connection,
@@ -806,6 +846,15 @@ public class ChildProcessLauncher {
                 return ChildProcessLauncher.getSurfaceTextureSurface(surfaceTextureId,
                         childProcessId);
             }
+
+            @Override
+            public void onDownloadStarted(boolean started, int downloadId) {
+                // TODO(qinmin): call native to cancel or proceed with the download.
+                if (callbackType != CALLBACK_FOR_DOWNLOAD_PROCESS) {
+                    Log.e(TAG, "Illegal callback for non-download process.");
+                    return;
+                }
+            }
         };
     }
 

content/public/android/java/src/org/chromium/content/common/ContentSwitches.java

@@ -72,6 +72,35 @@ public abstract class ContentSwitches {
     // Native switch kIPCSyncCompositing
     public static final String IPC_SYNC_COMPOSITING = "ipc-sync-compositing";
 
+    // Native switch kProcessType
+    public static final String SWITCH_PROCESS_TYPE = "type";
+
+    // Native switch kRendererProcess
+    public static final String SWITCH_RENDERER_PROCESS = "renderer";
+
+    // Native switch kUtilityProcess
+    public static final String SWITCH_UTILITY_PROCESS = "utility";
+
+    // Native switch kGPUProcess
+    public static final String SWITCH_GPU_PROCESS = "gpu-process";
+
+    // Native switch kDownloadProcess
+    public static final String SWITCH_DOWNLOAD_PROCESS = "download";
+
     // Prevent instantiation.
     private ContentSwitches() {}
+
+    public static String getSwitchValue(final String[] commandLine, String switchKey) {
+        if (commandLine == null || switchKey == null) {
+            return null;
+        }
+        // This format should be matched with the one defined in command_line.h.
+        final String switchKeyPrefix = "--" + switchKey + "=";
+        for (String command : commandLine) {
+            if (command != null && command.startsWith(switchKeyPrefix)) {
+                return command.substring(switchKeyPrefix.length());
+            }
+        }
+        return null;
+    }
 }

content/public/android/java/src/org/chromium/content/common/IChildProcessCallback.aidl

@@ -21,4 +21,8 @@ interface IChildProcessCallback {
   void unregisterSurfaceTextureSurface(int surfaceTextureId, int clientId);
 
   SurfaceWrapper getSurfaceTextureSurface(int surfaceTextureId);
+
+  // Callback to inform native that the download service has accepted or
+  // rejected the download.
+  void onDownloadStarted(boolean started, int downloadId);
 }

content/public/common/content_switches.cc

@@ -298,6 +298,9 @@ const char kDisableZeroCopy[]                = "disable-zero-copy";
 // based tests.
 const char kDomAutomationController[]       = "dom-automation";
 
+// Causes the process to run as a download subprocess.
+const char kDownloadProcess[]               = "download";
+
 // Enable antialiasing on 2d canvas clips (as opposed to draw operations)
 const char kEnable2dCanvasClipAntialiasing[] = "enable-2d-canvas-clip-aa";
 

content/public/common/content_switches.h

@@ -96,6 +96,7 @@ CONTENT_EXPORT extern const char kDisableWebSecurity[];
 extern const char kDisableXSSAuditor[];
 CONTENT_EXPORT extern const char kDisableZeroCopy[];
 CONTENT_EXPORT extern const char kDomAutomationController[];
+CONTENT_EXPORT extern const char kDownloadProcess[];
 extern const char kEnable2dCanvasClipAntialiasing[];
 CONTENT_EXPORT extern const char kEnableAggressiveDOMStorageFlushing[];
 CONTENT_EXPORT extern const char kEnableAudioSupportForDesktopShare[];