Separate out the backing store from the RenderWidgetHost into its own file to

make porting easier.

I also did some cleanup in the scrolling and painting areas, collapsing the
confusing ScrollRect call inside OnMsgScrollRect to just be inside the function
and call a new function on the backing store to scroll it. Same for painting.

This also moves plugin window moving to the view.
Review URL: http://codereview.chromium.org/18702

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@8594 0039d316-1c4b-4281-b951-d872f2087c98

8 files changed, 505 insertions, 366 deletions

diff --git a/chrome/browser/browser.vcproj b/chrome/browser/browser.vcproj
index 6995730..efb1ee4 100644
--- a/chrome/browser/browser.vcproj
+++ b/chrome/browser/browser.vcproj
@@ -1946,6 +1946,14 @@
 				>
 			</File>
 			<File
+				RelativePath=".\renderer_host\backing_store.cc"
+				>
+			</File>
+			<File
+				RelativePath=".\renderer_host\backing_store.h"
+				>
+			</File>
+			<File
 				RelativePath=".\renderer_host\browser_render_process_host.cc"
 				>
 			</File>
diff --git a/chrome/browser/renderer_host/backing_store.cc b/chrome/browser/renderer_host/backing_store.cc
new file mode 100644
index 0000000..c12d0bd
--- /dev/null
+++ b/chrome/browser/renderer_host/backing_store.cc
@@ -0,0 +1,243 @@
+// Copyright (c) 2006-2008 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 "chrome/browser/renderer_host/backing_store.h"

+

+#include "chrome/browser/renderer_host/render_widget_host.h"

+#include "chrome/common/win_util.h"

+

+#if defined(OS_WIN)

+#include "base/gfx/gdi_util.h"

+#endif

+

+namespace {

+

+typedef OwningMRUCache<RenderWidgetHost*, BackingStore*> BackingStoreCache;

+static BackingStoreCache* cache = NULL;

+

+// Returns the size of the backing store cache.

+// TODO(iyengar) Make this dynamic, i.e. based on the available resources

+// on the machine.

+static int GetBackingStoreCacheSize() {

+  const int kMaxSize = 5;

+  return kMaxSize;

+}

+

+// Creates the backing store for the host based on the dimensions passed in.

+// Removes the existing backing store if there is one.

+BackingStore* CreateBackingStore(RenderWidgetHost* host,

+                                 const gfx::Rect& backing_store_rect) {

+  BackingStoreManager::RemoveBackingStore(host);

+

+  BackingStore* backing_store = new BackingStore(backing_store_rect.size());

+  int backing_store_cache_size = GetBackingStoreCacheSize();

+  if (backing_store_cache_size > 0) {

+    if (!cache)

+      cache = new BackingStoreCache(backing_store_cache_size);

+    cache->Put(host, backing_store);

+  }

+  return backing_store;

+}

+

+}  // namespace

+

+#if defined(OS_WIN)

+

+// BackingStore (Windows) ------------------------------------------------------

+

+BackingStore::BackingStore(const gfx::Size& size)

+    : size_(size),

+      backing_store_dib_(NULL),

+      original_bitmap_(NULL) {

+  HDC screen_dc = ::GetDC(NULL);

+  hdc_ = CreateCompatibleDC(screen_dc);

+  ReleaseDC(NULL, screen_dc);

+}

+

+BackingStore::~BackingStore() {

+  DCHECK(hdc_);

+

+  DeleteDC(hdc_);

+

+  if (backing_store_dib_) {

+    DeleteObject(backing_store_dib_);

+    backing_store_dib_ = NULL;

+  }

+}

+

+bool BackingStore::PaintRect(base::ProcessHandle process,

+                             HANDLE bitmap_section,

+                             const gfx::Rect& bitmap_rect) {

+  // The bitmap received is valid only in the renderer process.

+  HANDLE valid_bitmap =

+      win_util::GetSectionFromProcess(bitmap_section, process, false);

+  if (!valid_bitmap)

+    return false;

+

+  if (!backing_store_dib_) {

+    backing_store_dib_ = CreateDIB(hdc_, size_.width(), size_.height(), true,

+                                   NULL);

+    DCHECK(backing_store_dib_ != NULL);

+    original_bitmap_ = SelectObject(hdc_, backing_store_dib_);

+  }

+

+  // TODO(darin): protect against integer overflow

+  DWORD size = 4 * bitmap_rect.width() * bitmap_rect.height();

+  void* backing_store_data = MapViewOfFile(valid_bitmap, FILE_MAP_READ, 0, 0,

+                                           size);

+  // These values are shared with gfx::PlatformDevice

+  BITMAPINFOHEADER hdr;

+  gfx::CreateBitmapHeader(bitmap_rect.width(), bitmap_rect.height(), &hdr);

+  // Account for a bitmap_rect that exceeds the bounds of our view

+  gfx::Rect view_rect(0, 0, size_.width(), size_.height());

+  gfx::Rect paint_rect = view_rect.Intersect(bitmap_rect);

+

+  StretchDIBits(hdc_,

+                paint_rect.x(),

+                paint_rect.y(),

+                paint_rect.width(),

+                paint_rect.height(),

+                0, 0,  // source x,y

+                paint_rect.width(),

+                paint_rect.height(),

+                backing_store_data,

+                reinterpret_cast<BITMAPINFO*>(&hdr),

+                DIB_RGB_COLORS,

+                SRCCOPY);

+

+  UnmapViewOfFile(backing_store_data);

+  CloseHandle(valid_bitmap);

+  return true;

+}

+

+void BackingStore::ScrollRect(base::ProcessHandle process,

+                              HANDLE bitmap, const gfx::Rect& bitmap_rect,

+                              int dx, int dy,

+                              const gfx::Rect& clip_rect,

+                              const gfx::Size& view_size) {

+  RECT damaged_rect, r = clip_rect.ToRECT();

+  ScrollDC(hdc_, dx, dy, NULL, &r, NULL, &damaged_rect);

+

+  // TODO(darin): this doesn't work if dx and dy are both non-zero!

+  DCHECK(dx == 0 || dy == 0);

+

+  // We expect that damaged_rect should equal bitmap_rect.

+  DCHECK(gfx::Rect(damaged_rect) == bitmap_rect);

+

+  PaintRect(process, bitmap, bitmap_rect);

+}

+

+HANDLE BackingStore::CreateDIB(HDC dc,

+                               int width, int height,

+                               bool use_system_color_depth,

+                               HANDLE section) {

+  BITMAPINFOHEADER hdr;

+

+  if (use_system_color_depth) {

+    HDC screen_dc = ::GetDC(NULL);

+    int color_depth = GetDeviceCaps(screen_dc, BITSPIXEL);

+    ::ReleaseDC(NULL, screen_dc);

+

+    // Color depths less than 16 bpp require a palette to be specified in the

+    // BITMAPINFO structure passed to CreateDIBSection. Instead of creating

+    // the palette, we specify the desired color depth as 16 which allows the

+    // OS to come up with an approximation. Tested this with 8bpp.

+    if (color_depth < 16)

+      color_depth = 16;

+

+    gfx::CreateBitmapHeaderWithColorDepth(width, height, color_depth, &hdr);

+  } else {

+    gfx::CreateBitmapHeader(width, height, &hdr);

+  }

+  void* data = NULL;

+  HANDLE dib =

+      CreateDIBSection(hdc_, reinterpret_cast<BITMAPINFO*>(&hdr),

+                       0, &data, section, 0);

+  return dib;

+}

+

+#elif defined(OS_LINUX)

+

+// BackingStore (Linux) --------------------------------------------------------

+

+

+

+#elif defined(OS_MAC)

+

+// BackingStore (Mac) ----------------------------------------------------------

+

+

+

+#endif

+

+// BackingStoreManager ---------------------------------------------------------

+

+// static

+BackingStore* BackingStoreManager::GetBackingStore(

+    RenderWidgetHost* host,

+    const gfx::Size& desired_size) {

+  BackingStore* backing_store = Lookup(host);

+  if (backing_store) {

+    // If we already have a backing store, then make sure it is the correct

+    // size.

+    if (backing_store->size() == desired_size)

+      return backing_store;

+    backing_store = NULL;

+  }

+

+  return backing_store;

+}

+

+// static

+BackingStore* BackingStoreManager::PrepareBackingStore(

+    RenderWidgetHost* host,

+    const gfx::Rect& backing_store_rect,

+    HANDLE process_handle,

+    HANDLE bitmap_section,

+    const gfx::Rect& bitmap_rect,

+    bool* needs_full_paint) {

+  BackingStore* backing_store = GetBackingStore(host,

+                                                backing_store_rect.size());

+  if (!backing_store) {

+    // We need to get Webkit to generate a new paint here, as we

+    // don't have a previous snapshot.

+    if (bitmap_rect != backing_store_rect) {

+      DCHECK(needs_full_paint != NULL);

+      *needs_full_paint = true;

+    }

+    backing_store = CreateBackingStore(host, backing_store_rect);

+  }

+

+  DCHECK(backing_store != NULL);

+  backing_store->PaintRect(process_handle, bitmap_section, bitmap_rect);

+  return backing_store;

+}

+

+// static

+BackingStore* BackingStoreManager::Lookup(RenderWidgetHost* host) {

+  if (cache) {

+    BackingStoreCache::iterator it = cache->Peek(host);

+    if (it != cache->end())

+      return it->second;

+  }

+  return NULL;

+}

+

+// static

+void BackingStoreManager::RemoveBackingStore(RenderWidgetHost* host) {

+  if (!cache)

+    return;

+

+  BackingStoreCache::iterator it = cache->Peek(host);

+  if (it == cache->end())

+    return;

+

+  cache->Erase(it);

+

+  if (cache->empty()) {

+    delete cache;

+    cache = NULL;

+  }

+}

+

diff --git a/chrome/browser/renderer_host/backing_store.h b/chrome/browser/renderer_host/backing_store.h
new file mode 100644
index 0000000..07ed517
--- /dev/null
+++ b/chrome/browser/renderer_host/backing_store.h
@@ -0,0 +1,130 @@
+// Copyright (c) 2006-2008 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.

+

+#ifndef CHROME_BROWSER_RENDERER_HOST_BACKING_STORE_H_

+#define CHROME_BROWSER_RENDERER_HOST_BACKING_STORE_H_

+

+#include "base/basictypes.h"

+#include "base/gfx/rect.h"

+#include "base/gfx/size.h"

+#include "base/process.h"

+#include "build/build_config.h"

+#include "chrome/common/mru_cache.h"

+

+#if defined(OS_WIN)

+#include <windows.h>

+#endif

+

+class RenderWidgetHost;

+

+// BackingStore ----------------------------------------------------------------

+

+// Represents a backing store for the pixels in a RenderWidgetHost.

+class BackingStore {

+ public:

+  BackingStore(const gfx::Size& size);

+  ~BackingStore();

+

+  const gfx::Size& size() { return size_; }

+

+#if defined(OS_WIN)

+  HDC hdc() { return hdc_; }

+#endif

+

+  // Paints the bitmap from the renderer onto the backing store.

+  // TODO(port): The HANDLE is a shared section on Windows. Abstract this.

+  bool PaintRect(base::ProcessHandle process,

+                 HANDLE bitmap_section,

+                 const gfx::Rect& bitmap_rect);

+

+  // Scrolls the given rect in the backing store, replacing the given region

+  // identified by |bitmap_rect| by the bitmap in the file identified by the

+  // given file handle.

+  // TODO(port): The HANDLE is a shared section on Windows. Abstract this.

+  void ScrollRect(base::ProcessHandle process,

+                  HANDLE bitmap, const gfx::Rect& bitmap_rect,

+                  int dx, int dy,

+                  const gfx::Rect& clip_rect,

+                  const gfx::Size& view_size);

+

+ private:

+  // The size of the backing store.

+  gfx::Size size_;

+

+#if defined(OS_WIN)

+  // Creates a dib conforming to the height/width/section parameters passed

+  // in. The use_os_color_depth parameter controls whether we use the color

+  // depth to create an appropriate dib or not.

+  HANDLE CreateDIB(HDC dc,

+                   int width, int height,

+                   bool use_os_color_depth,

+                   HANDLE section);

+

+  // The backing store dc.

+  HDC hdc_;

+

+  // Handle to the backing store dib.

+  HANDLE backing_store_dib_;

+

+  // Handle to the original bitmap in the dc.

+  HANDLE original_bitmap_;

+#endif

+

+  DISALLOW_COPY_AND_ASSIGN(BackingStore);

+};

+

+// BackingStoreManager ---------------------------------------------------------

+

+// This class manages backing stores in the browsr. Every RenderWidgetHost is

+// associated with a backing store which it requests from this class.  The

+// hosts don't maintain any references to the backing stores.  These backing

+// stores are maintained in a cache which can be trimmed as needed.

+class BackingStoreManager {

+ public:

+  // Returns a backing store which matches the desired dimensions.

+  //

+  // backing_store_rect

+  //   The desired backing store dimensions.

+  // Returns a pointer to the backing store on success, NULL on failure.

+  static BackingStore* GetBackingStore(RenderWidgetHost* host,

+                                       const gfx::Size& desired_size);

+

+  // Returns a backing store which is fully ready for consumption, i.e. the

+  // bitmap from the renderer has been copied into the backing store dc, or the

+  // bitmap in the backing store dc references the renderer bitmap.

+  //

+  // backing_store_rect

+  //   The desired backing store dimensions.

+  // process_handle

+  //   The renderer process handle.

+  // bitmap_section

+  //   The bitmap section from the renderer.

+  // bitmap_rect

+  //   The rect to be painted into the backing store

+  // needs_full_paint

+  //   Set if we need to send out a request to paint the view

+  //   to the renderer.

+  // TODO(port): The HANDLE is a shared section on Windows. Abstract this.

+  static BackingStore* PrepareBackingStore(RenderWidgetHost* host,

+                                           const gfx::Rect& backing_store_rect,

+                                           base::ProcessHandle process_handle,

+                                           HANDLE bitmap_section,

+                                           const gfx::Rect& bitmap_rect,

+                                           bool* needs_full_paint);

+

+  // Returns a matching backing store for the host.

+  // Returns NULL if we fail to find one.

+  static BackingStore* Lookup(RenderWidgetHost* host);

+

+  // Removes the backing store for the host.

+  static void RemoveBackingStore(RenderWidgetHost* host);

+

+ private:

+  // Not intended for instantiation.

+  BackingStoreManager() {}

+

+  DISALLOW_COPY_AND_ASSIGN(BackingStoreManager);

+};

+

+#endif  // CHROME_BROWSER_RENDERER_HOST_BACKING_STORE_H_

diff --git a/chrome/browser/renderer_host/render_widget_host.cc b/chrome/browser/renderer_host/render_widget_host.cc
index 354f54b..63dd0f3 100644
--- a/chrome/browser/renderer_host/render_widget_host.cc
+++ b/chrome/browser/renderer_host/render_widget_host.cc
@@ -7,10 +7,10 @@
 #include "base/gfx/gdi_util.h"
 #include "base/message_loop.h"
 #include "chrome/app/chrome_dll_resource.h"
+#include "chrome/browser/renderer_host/backing_store.h"
 #include "chrome/browser/renderer_host/render_process_host.h"
 #include "chrome/browser/renderer_host/render_widget_helper.h"
 #include "chrome/browser/renderer_host/render_widget_host_view.h"
-#include "chrome/common/mru_cache.h"
 #include "chrome/common/notification_service.h"
 #include "chrome/common/win_util.h"
 #include "chrome/views/view.h"
@@ -31,241 +31,6 @@ static const int kPaintMsgTimeoutMS = 40;
 static const int kHungRendererDelayMs = 20000;
 
 ///////////////////////////////////////////////////////////////////////////////
-// RenderWidget::BackingStore
-
-RenderWidgetHost::BackingStore::BackingStore(const gfx::Size& size)
-    : size_(size),
-      backing_store_dib_(NULL),
-      original_bitmap_(NULL) {
-  HDC screen_dc = ::GetDC(NULL);
-  hdc_ = CreateCompatibleDC(screen_dc);
-  ReleaseDC(NULL, screen_dc);
-}
-
-RenderWidgetHost::BackingStore::~BackingStore() {
-  DCHECK(hdc_);
-
-  DeleteDC(hdc_);
-
-  if (backing_store_dib_) {
-    DeleteObject(backing_store_dib_);
-    backing_store_dib_ = NULL;
-  }
-}
-
-bool RenderWidgetHost::BackingStore::Refresh(HANDLE process, 
-                                             HANDLE bitmap_section,
-                                             const gfx::Rect& bitmap_rect) {
-  // The bitmap received is valid only in the renderer process.
-  HANDLE valid_bitmap =
-      win_util::GetSectionFromProcess(bitmap_section, process, false);
-  if (!valid_bitmap)
-    return false;
-
-  if (!backing_store_dib_) {
-    backing_store_dib_ = CreateDIB(hdc_, size_.width(), size_.height(), true,
-                                   NULL);
-    DCHECK(backing_store_dib_ != NULL);
-    original_bitmap_ = SelectObject(hdc_, backing_store_dib_);
-  }
-
-  // TODO(darin): protect against integer overflow
-  DWORD size = 4 * bitmap_rect.width() * bitmap_rect.height();
-  void* backing_store_data = MapViewOfFile(valid_bitmap, FILE_MAP_READ, 0, 0,
-                                           size);
-  // These values are shared with gfx::PlatformDevice
-  BITMAPINFOHEADER hdr;
-  gfx::CreateBitmapHeader(bitmap_rect.width(), bitmap_rect.height(), &hdr);
-  // Account for a bitmap_rect that exceeds the bounds of our view
-  gfx::Rect view_rect(0, 0, size_.width(), size_.height());
-  gfx::Rect paint_rect = view_rect.Intersect(bitmap_rect);
-
-  StretchDIBits(hdc_,
-                paint_rect.x(),
-                paint_rect.y(),
-                paint_rect.width(),
-                paint_rect.height(),
-                0, 0,  // source x,y
-                paint_rect.width(),
-                paint_rect.height(),
-                backing_store_data,
-                reinterpret_cast<BITMAPINFO*>(&hdr),
-                DIB_RGB_COLORS,
-                SRCCOPY);
-
-  UnmapViewOfFile(backing_store_data);
-  CloseHandle(valid_bitmap);
-  return true;
-}
-
-HANDLE RenderWidgetHost::BackingStore::CreateDIB(HDC dc, int width, int height,
-                                                 bool use_system_color_depth,
-                                                 HANDLE section) {
-  BITMAPINFOHEADER hdr;
-
-  if (use_system_color_depth) {
-    HDC screen_dc = ::GetDC(NULL);
-    int color_depth = GetDeviceCaps(screen_dc, BITSPIXEL);
-    ::ReleaseDC(NULL, screen_dc);
-
-    // Color depths less than 16 bpp require a palette to be specified in the
-    // BITMAPINFO structure passed to CreateDIBSection. Instead of creating
-    // the palette, we specify the desired color depth as 16 which allows the
-    // OS to come up with an approximation. Tested this with 8bpp.
-    if (color_depth < 16)
-      color_depth = 16;
-
-    gfx::CreateBitmapHeaderWithColorDepth(width, height, color_depth, &hdr);
-  } else {
-    gfx::CreateBitmapHeader(width, height, &hdr);
-  }
-  void* data = NULL;
-  HANDLE dib =
-      CreateDIBSection(hdc_, reinterpret_cast<BITMAPINFO*>(&hdr),
-                       0, &data, section, 0);
-  return dib;
-}
-
-
-///////////////////////////////////////////////////////////////////////////////
-// RenderWidgetHost::BackingStoreManager
-
-// This class manages backing stores in the browsr. Every RenderWidgetHost
-// is associated with a backing store which it requests from this class.
-// The hosts don't maintain any references to the backing stores. 
-// These backing stores are maintained in a cache which can be trimmed as
-// needed.
-class RenderWidgetHost::BackingStoreManager {
- public:
-  // Returns a backing store which matches the desired dimensions.
-  // Parameters:
-  // host
-  //  A pointer to the RenderWidgetHost.
-  // backing_store_rect
-  //  The desired backing store dimensions.
-  // Returns a pointer to the backing store on success, NULL on failure.
-  static BackingStore* GetBackingStore(RenderWidgetHost* host,
-                                       const gfx::Size& desired_size) {
-    BackingStore* backing_store = Lookup(host);
-    if (backing_store) {
-      // If we already have a backing store, then make sure it is the correct
-      // size.
-      if (backing_store->size() == desired_size)
-        return backing_store;
-      backing_store = NULL;
-    }
-
-    return backing_store;
-  }
-
-  // Returns a backing store which is fully ready for consumption,
-  // i.e. the bitmap from the renderer has been copied into the
-  // backing store dc, or the bitmap in the backing store dc references
-  // the renderer bitmap.
-  // Parameters:
-  // host
-  //   A pointer to the RenderWidgetHost.
-  // backing_store_rect
-  //   The desired backing store dimensions.
-  // process_handle
-  //   The renderer process handle.
-  // bitmap_section
-  //   The bitmap section from the renderer.
-  // bitmap_rect
-  //   The rect to be painted into the backing store
-  // needs_full_paint
-  //   Set if we need to send out a request to paint the view
-  //   to the renderer.
-  static BackingStore* PrepareBackingStore(RenderWidgetHost* host, 
-                                           const gfx::Rect& backing_store_rect,
-                                           HANDLE process_handle,
-                                           HANDLE bitmap_section,
-                                           const gfx::Rect& bitmap_rect,
-                                           bool* needs_full_paint) {
-    BackingStore* backing_store = GetBackingStore(host,
-                                                  backing_store_rect.size());
-    if (!backing_store) {
-      // We need to get Webkit to generate a new paint here, as we
-      // don't have a previous snapshot.
-      if (bitmap_rect != backing_store_rect) {
-        DCHECK(needs_full_paint != NULL);
-        *needs_full_paint = true;
-      }
-      backing_store = CreateBackingStore(host, backing_store_rect);
-    }
-
-    DCHECK(backing_store != NULL);
-    backing_store->Refresh(process_handle, bitmap_section, bitmap_rect);
-    return backing_store;
-  }
-
-  // Returns a matching backing store for the host.
-  // Returns NULL if we fail to find one.
-  static BackingStore* Lookup(RenderWidgetHost* host) {
-    if (cache_) {
-      BackingStoreCache::iterator it = cache_->Peek(host);
-      if (it != cache_->end())
-        return it->second;
-    }
-    return NULL;
-  }
-
-  // Removes the backing store for the host.
-  static void RemoveBackingStore(RenderWidgetHost* host) {
-    if (!cache_)
-      return;
-
-    BackingStoreCache::iterator it = cache_->Peek(host);
-    if (it == cache_->end())
-      return;
-
-    cache_->Erase(it);
-
-    if (cache_->empty()) {
-      delete cache_;
-      cache_ = NULL;
-    }
-  }
-
- private:
-   // Not intended for instantiation.
-  ~BackingStoreManager();
-
-  typedef OwningMRUCache<RenderWidgetHost*, BackingStore*> BackingStoreCache;
-  static BackingStoreCache* cache_;
-
-  // Returns the size of the backing store cache.
-  // TODO(iyengar) Make this dynamic, i.e. based on the available resources
-  // on the machine.
-  static int GetBackingStoreCacheSize() {
-    const int kMaxSize = 5;
-    return kMaxSize;
-  }
-
-  // Creates the backing store for the host based on the dimensions passed in.
-  // Removes the existing backing store if there is one.
-  static BackingStore* CreateBackingStore(
-      RenderWidgetHost* host, const gfx::Rect& backing_store_rect) {
-    RemoveBackingStore(host);
-
-    BackingStore* backing_store = new BackingStore(backing_store_rect.size());
-    int backing_store_cache_size = GetBackingStoreCacheSize();
-    if (backing_store_cache_size > 0) {
-      if (!cache_)
-        cache_ = new BackingStoreCache(backing_store_cache_size);
-      cache_->Put(host, backing_store);
-    }
-    return backing_store;
-  }
-
-  DISALLOW_EVIL_CONSTRUCTORS(BackingStoreManager);
-};
-
-RenderWidgetHost::BackingStoreManager::BackingStoreCache* 
-    RenderWidgetHost::BackingStoreManager::cache_ = NULL;
-
-
-///////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHost
 
 RenderWidgetHost::RenderWidgetHost(RenderProcessHost* process,
@@ -375,17 +140,27 @@ void RenderWidgetHost::OnMsgPaintRect(
   DCHECK(!params.bitmap_rect.IsEmpty());
   DCHECK(!params.view_size.IsEmpty());
 
-  PaintRect(params.bitmap, params.bitmap_rect, params.view_size);
+  // Paint the backing store. This will update it with the renderer-supplied
+  // bits. The view will read out of the backing store later to actually draw
+  // to the screen.
+  PaintBackingStoreRect(params.bitmap, params.bitmap_rect, params.view_size);
 
   // ACK early so we can prefetch the next PaintRect if there is a next one.
+  // This must be done AFTER we're done painting with the bitmap supplied by the
+  // renderer. This ACK is a signal to the renderer that the backing store can
+  // be re-used, so the bitmap may be invalid after this call.
   Send(new ViewMsg_PaintRect_ACK(routing_id_));
 
-  // TODO(darin): This should really be done by the view_!
-  MovePluginWindows(params.plugin_window_moves);
+  // We don't need to update the view if the view is hidden. We must do this
+  // early return after the ACK is sent, however, or the renderer will not send
+  // is more data.
+  if (is_hidden_)
+    return;
 
-  // The view might be destroyed already.  Check for this case.
+  // Now paint the view. Watch out: it might be destroyed already.
   if (view_ && !suppress_view_updating_) {
     view_being_painted_ = true;
+    view_->MovePluginWindows(params.plugin_window_moves);
     view_->DidPaintRect(params.bitmap_rect);
     view_being_painted_ = false;
   }
@@ -413,18 +188,27 @@ void RenderWidgetHost::OnMsgScrollRect(
 
   DCHECK(!params.view_size.IsEmpty());
 
-  ScrollRect(params.bitmap, params.bitmap_rect, params.dx, params.dy,
-             params.clip_rect, params.view_size);
+  // Scroll the backing store.
+  ScrollBackingStoreRect(params.bitmap, params.bitmap_rect,
+                         params.dx, params.dy,
+                         params.clip_rect, params.view_size);
 
   // ACK early so we can prefetch the next ScrollRect if there is a next one.
+  // This must be done AFTER we're done painting with the bitmap supplied by the
+  // renderer. This ACK is a signal to the renderer that the backing store can
+  // be re-used, so the bitmap may be invalid after this call.
   Send(new ViewMsg_ScrollRect_ACK(routing_id_));
 
-  // TODO(darin): This should really be done by the view_!
-  MovePluginWindows(params.plugin_window_moves);
+  // We don't need to update the view if the view is hidden. We must do this
+  // early return after the ACK is sent, however, or the renderer will not send
+  // is more data.
+  if (is_hidden_)
+    return;
 
-  // The view might be destroyed already. Check for this case
+  // Paint the view. Watch out: it might be destroyed already.
   if (view_) {
     view_being_painted_ = true;
+    view_->MovePluginWindows(params.plugin_window_moves);
     view_->DidScrollRect(params.clip_rect, params.dx, params.dy);
     view_being_painted_ = false;
   }
@@ -434,53 +218,6 @@ void RenderWidgetHost::OnMsgScrollRect(
   UMA_HISTOGRAM_TIMES(L"MPArch.RWH_OnMsgScrollRect", delta);
 }
 
-void RenderWidgetHost::MovePluginWindows(
-    const std::vector<WebPluginGeometry>& plugin_window_moves) {
-  if (plugin_window_moves.empty())
-    return;
-
-  HDWP defer_window_pos_info =
-      ::BeginDeferWindowPos(static_cast<int>(plugin_window_moves.size()));
-
-  if (!defer_window_pos_info) {
-    NOTREACHED();
-    return;
-  }
-
-  for (size_t i = 0; i < plugin_window_moves.size(); ++i) {
-    unsigned long flags = 0;
-    const WebPluginGeometry& move = plugin_window_moves[i];
-
-    if (move.visible)
-      flags |= SWP_SHOWWINDOW;
-    else
-      flags |= SWP_HIDEWINDOW;
-
-    HRGN hrgn = ::CreateRectRgn(move.clip_rect.x(),
-                                move.clip_rect.y(),
-                                move.clip_rect.right(),
-                                move.clip_rect.bottom());
-    gfx::SubtractRectanglesFromRegion(hrgn, move.cutout_rects);
-
-    // Note: System will own the hrgn after we call SetWindowRgn,
-    // so we don't need to call DeleteObject(hrgn)
-    ::SetWindowRgn(move.window, hrgn, !move.clip_rect.IsEmpty());
-
-    defer_window_pos_info = ::DeferWindowPos(defer_window_pos_info,
-                                             move.window, NULL,
-                                             move.window_rect.x(),
-                                             move.window_rect.y(),
-                                             move.window_rect.width(),
-                                             move.window_rect.height(), flags);
-    if (!defer_window_pos_info) {
-      DCHECK(false) << "DeferWindowPos given invalid window, so rest ignored.";
-      return;
-    }
-  }
-
-  ::EndDeferWindowPos(defer_window_pos_info);
-}
-
 void RenderWidgetHost::OnMsgInputEventAck(const IPC::Message& message) {
   // Log the time delta for processing an input event.
   TimeDelta delta = TimeTicks::Now() - input_event_start_time_;
@@ -726,7 +463,7 @@ void RenderWidgetHost::SetIsLoading(bool is_loading) {
   view_->SetIsLoading(is_loading);
 }
 
-RenderWidgetHost::BackingStore* RenderWidgetHost::GetBackingStore() {
+BackingStore* RenderWidgetHost::GetBackingStore() {
   // We should not be asked to paint while we are hidden.  If we are hidden,
   // then it means that our consumer failed to call WasRestored.
   DCHECK(!is_hidden_) << "GetBackingStore called while hidden!";
@@ -761,9 +498,13 @@ RenderWidgetHost::BackingStore* RenderWidgetHost::GetBackingStore() {
   return backing_store;
 }
 
-void RenderWidgetHost::PaintRect(HANDLE bitmap, const gfx::Rect& bitmap_rect,
-                                 const gfx::Size& view_size) {
+void RenderWidgetHost::PaintBackingStoreRect(HANDLE bitmap,
+                                             const gfx::Rect& bitmap_rect,
+                                             const gfx::Size& view_size) {
   if (is_hidden_) {
+    // Don't bother updating the backing store when we're hidden. Just mark it
+    // as being totally invalid. This will cause a complete repaint when the
+    // view is restored.
     needs_repainting_on_restore_ = true;
     return;
   }
@@ -786,10 +527,15 @@ void RenderWidgetHost::PaintRect(HANDLE bitmap, const gfx::Rect& bitmap_rect,
   }
 }
 
-void RenderWidgetHost::ScrollRect(HANDLE bitmap, const gfx::Rect& bitmap_rect,
-                                  int dx, int dy, const gfx::Rect& clip_rect,
-                                  const gfx::Size& view_size) {
+void RenderWidgetHost::ScrollBackingStoreRect(HANDLE bitmap,
+                                              const gfx::Rect& bitmap_rect,
+                                              int dx, int dy,
+                                              const gfx::Rect& clip_rect,
+                                              const gfx::Size& view_size) {
   if (is_hidden_) {
+    // Don't bother updating the backing store when we're hidden. Just mark it
+    // as being totally invalid. This will cause a complete repaint when the
+    // view is restored.
     needs_repainting_on_restore_ = true;
     return;
   }
@@ -800,19 +546,11 @@ void RenderWidgetHost::ScrollRect(HANDLE bitmap, const gfx::Rect& bitmap_rect,
   BackingStore* backing_store = BackingStoreManager::Lookup(this);
   if (!backing_store || (backing_store->size() != view_size))
     return;
-
-  RECT damaged_rect, r = clip_rect.ToRECT();
-  ScrollDC(backing_store->dc(), dx, dy, NULL, &r, NULL, &damaged_rect);
-
-  // TODO(darin): this doesn't work if dx and dy are both non-zero!
-  DCHECK(dx == 0 || dy == 0);
-
-  // We expect that damaged_rect should equal bitmap_rect.
-  DCHECK(gfx::Rect(damaged_rect) == bitmap_rect);
-
-  backing_store->Refresh(process_->process().handle(), bitmap, bitmap_rect);
+  backing_store->ScrollRect(process_->process().handle(), bitmap, bitmap_rect,
+                            dx, dy, clip_rect, view_size);
 }
 
+
 void RenderWidgetHost::RestartHangMonitorTimeout() {
   StartHangMonitorTimeout(TimeDelta::FromMilliseconds(kHungRendererDelayMs));
 }
diff --git a/chrome/browser/renderer_host/render_widget_host.h b/chrome/browser/renderer_host/render_widget_host.h
index d683e84..5992b69 100644
--- a/chrome/browser/renderer_host/render_widget_host.h
+++ b/chrome/browser/renderer_host/render_widget_host.h
@@ -157,13 +157,6 @@ class RenderWidgetHost : public IPC::Channel::Listener {
   // Indicates if the page has finished loading.
   virtual void SetIsLoading(bool is_loading);
 
-  // Represents a device-dependent drawing surface used to hold the rendering
-  // of a RenderWidgetHost.
-  class BackingStore;
-
-  // Manages a set of backing stores.
-  class BackingStoreManager;
-
   // Get access to the widget's backing store.  If a resize is in progress,
   // then the current size of the backing store may be less than the size of
   // the widget's view.  This method returns NULL if the backing store could
@@ -226,9 +219,6 @@ class RenderWidgetHost : public IPC::Channel::Listener {
   void OnMsgImeUpdateStatus(ViewHostMsg_ImeControl control,
                             const gfx::Rect& caret_rect);
 
-  void MovePluginWindows(
-      const std::vector<WebPluginGeometry>& plugin_window_moves);
-
   // TODO(beng): (Cleanup) remove this friendship once we expose a clean API to
   // RenderWidgetHost Views. This exists only to give RenderWidgetHostView
   // access to Forward*Event.
@@ -239,14 +229,6 @@ class RenderWidgetHost : public IPC::Channel::Listener {
   void ForwardWheelEvent(const WebMouseWheelEvent& wheel_event);
   void ForwardInputEvent(const WebInputEvent& input_event, int event_size);
 
-  // Called to paint a region of the backing store
-  void PaintRect(HANDLE bitmap, const gfx::Rect& bitmap_rect,
-                 const gfx::Size& view_size);
-
-  // Called to scroll a region of the backing store
-  void ScrollRect(HANDLE bitmap, const gfx::Rect& bitmap_rect, int dx, int dy,
-                  const gfx::Rect& clip_rect, const gfx::Size& view_size);
-
   // Tell this object to destroy itself.
   void Destroy();
 
@@ -324,38 +306,22 @@ class RenderWidgetHost : public IPC::Channel::Listener {
   // operation to finish.
   base::TimeTicks repaint_start_time_;
 
-  DISALLOW_EVIL_CONSTRUCTORS(RenderWidgetHost);
-};
-
-class RenderWidgetHost::BackingStore {
- public:
-  BackingStore(const gfx::Size& size);
-  ~BackingStore();
-
-  HDC dc() { return hdc_; }
-  const gfx::Size& size() { return size_; }
-
-  // Paints the bitmap from the renderer onto the backing store.
-  bool Refresh(HANDLE process, HANDLE bitmap_section,
-               const gfx::Rect& bitmap_rect);
-
  private:
-  // Creates a dib conforming to the height/width/section parameters passed
-  // in. The use_os_color_depth parameter controls whether we use the color
-  // depth to create an appropriate dib or not.
-  HANDLE CreateDIB(HDC dc, int width, int height, bool use_os_color_depth, 
-                   HANDLE section);
-
-  // The backing store dc.
-  HDC hdc_;
-  // The size of the backing store.
-  gfx::Size size_;
-  // Handle to the backing store dib.
-  HANDLE backing_store_dib_;
-  // Handle to the original bitmap in the dc.
-  HANDLE original_bitmap_;
-
-  DISALLOW_COPY_AND_ASSIGN(BackingStore);
+  // Paints the given bitmap to the current backing store at the given location.
+  void PaintBackingStoreRect(HANDLE bitmap,
+                             const gfx::Rect& bitmap_rect,
+                             const gfx::Size& view_size);
+
+  // Scrolls the given |clip_rect| in the backing by the given dx/dy amount. The
+  // |bitmap| and its corresponding location |bitmap_rect| in the backing store
+  // is the newly painted pixels by the renderer.
+  void ScrollBackingStoreRect(HANDLE bitmap,
+                              const gfx::Rect& bitmap_rect,
+                              int dx, int dy,
+                              const gfx::Rect& clip_rect,
+                              const gfx::Size& view_size);
+
+  DISALLOW_COPY_AND_ASSIGN(RenderWidgetHost);
 };
 
 class RenderWidgetHost::PaintObserver {
@@ -366,4 +332,4 @@ class RenderWidgetHost::PaintObserver {
   virtual void RenderWidgetHostDidPaint(RenderWidgetHost* rwh) = 0;
 };
 
-#endif  // #ifndef CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_H_
+#endif  // CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_H_
diff --git a/chrome/browser/renderer_host/render_widget_host_view.h b/chrome/browser/renderer_host/render_widget_host_view.h
index 8e6152f..1a3facfa 100644
--- a/chrome/browser/renderer_host/render_widget_host_view.h
+++ b/chrome/browser/renderer_host/render_widget_host_view.h
@@ -59,6 +59,10 @@ class RenderWidgetHostView {
   // Retrieves the HWND used to contain plugin HWNDs.
   virtual HWND GetPluginHWND() = 0;
 
+  // Moves all plugin windows as described in the given list.
+  virtual void MovePluginWindows(
+      const std::vector<WebPluginGeometry>& plugin_window_moves) = 0;
+
   // Sends the specified mouse event to the renderer.
   virtual void ForwardMouseEventToRenderer(UINT message,
                                            WPARAM wparam,
@@ -92,10 +96,14 @@ class RenderWidgetHostView {
                                const gfx::Rect& caret_rect) = 0;
 
   // Informs the view that a portion of the widget's backing store was painted.
+  // The view should copy the given rect from the backing store of the render
+  // widget onto the screen.
   virtual void DidPaintRect(const gfx::Rect& rect) = 0;
 
   // Informs the view that a portion of the widget's backing store was scrolled
-  // by dx pixels horizontally and dy pixels vertically.
+  // by dx pixels horizontally and dy pixels vertically. The view should copy
+  // the exposed pixels from the backing store of the render widget (which has
+  // already been scrolled) onto the screen.
   virtual void DidScrollRect(
       const gfx::Rect& rect, int dx, int dy) = 0;
 
diff --git a/chrome/browser/renderer_host/render_widget_host_view_win.cc b/chrome/browser/renderer_host/render_widget_host_view_win.cc
index f628809..eacf329 100644
--- a/chrome/browser/renderer_host/render_widget_host_view_win.cc
+++ b/chrome/browser/renderer_host/render_widget_host_view_win.cc
@@ -12,10 +12,8 @@
 #include "chrome/browser/browser_accessibility.h"
 #include "chrome/browser/browser_accessibility_manager.h"
 #include "chrome/browser/browser_trial.h"
+#include "chrome/browser/renderer_host/backing_store.h"
 #include "chrome/browser/renderer_host/render_process_host.h"
-// TODO(beng): (Cleanup) we should not need to include this file... see comment
-//             in |DidBecomeSelected|.
-#include "chrome/browser/renderer_host/render_view_host.h"
 #include "chrome/browser/renderer_host/render_widget_host.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_switches.h"
@@ -143,6 +141,53 @@ HWND RenderWidgetHostViewWin::GetPluginHWND() {
   return m_hWnd;
 }
 
+void RenderWidgetHostViewWin::MovePluginWindows(
+    const std::vector<WebPluginGeometry>& plugin_window_moves) {
+  if (plugin_window_moves.empty())
+    return;
+
+  HDWP defer_window_pos_info =
+      ::BeginDeferWindowPos(static_cast<int>(plugin_window_moves.size()));
+
+  if (!defer_window_pos_info) {
+    NOTREACHED();
+    return;
+  }
+
+  for (size_t i = 0; i < plugin_window_moves.size(); ++i) {
+    unsigned long flags = 0;
+    const WebPluginGeometry& move = plugin_window_moves[i];
+
+    if (move.visible)
+      flags |= SWP_SHOWWINDOW;
+    else
+      flags |= SWP_HIDEWINDOW;
+
+    HRGN hrgn = ::CreateRectRgn(move.clip_rect.x(),
+                                move.clip_rect.y(),
+                                move.clip_rect.right(),
+                                move.clip_rect.bottom());
+    gfx::SubtractRectanglesFromRegion(hrgn, move.cutout_rects);
+
+    // Note: System will own the hrgn after we call SetWindowRgn,
+    // so we don't need to call DeleteObject(hrgn)
+    ::SetWindowRgn(move.window, hrgn, !move.clip_rect.IsEmpty());
+
+    defer_window_pos_info = ::DeferWindowPos(defer_window_pos_info,
+                                             move.window, NULL,
+                                             move.window_rect.x(),
+                                             move.window_rect.y(),
+                                             move.window_rect.width(),
+                                             move.window_rect.height(), flags);
+    if (!defer_window_pos_info) {
+      DCHECK(false) << "DeferWindowPos given invalid window, so rest ignored.";
+      return;
+    }
+  }
+
+  ::EndDeferWindowPos(defer_window_pos_info);
+}
+
 void RenderWidgetHostViewWin::ForwardMouseEventToRenderer(UINT message,
                                                          WPARAM wparam,
                                                          LPARAM lparam) {
@@ -401,8 +446,7 @@ void RenderWidgetHostViewWin::OnPaint(HDC dc) {
   CPaintDC paint_dc(m_hWnd);
   HBRUSH white_brush = reinterpret_cast<HBRUSH>(GetStockObject(WHITE_BRUSH));
 
-  RenderWidgetHost::BackingStore* backing_store =
-      render_widget_host_->GetBackingStore();
+  BackingStore* backing_store = render_widget_host_->GetBackingStore();
 
   if (backing_store) {
     gfx::Rect damaged_rect(paint_dc.m_ps.rcPaint);
@@ -417,7 +461,7 @@ void RenderWidgetHostViewWin::OnPaint(HDC dc) {
              paint_rect.y(),
              paint_rect.width(),
              paint_rect.height(),
-             backing_store->dc(),
+             backing_store->hdc(),
              paint_rect.x(),
              paint_rect.y(),
              SRCCOPY);
diff --git a/chrome/browser/renderer_host/render_widget_host_view_win.h b/chrome/browser/renderer_host/render_widget_host_view_win.h
index a735ab0..e8456be 100644
--- a/chrome/browser/renderer_host/render_widget_host_view_win.h
+++ b/chrome/browser/renderer_host/render_widget_host_view_win.h
@@ -125,6 +125,8 @@ class RenderWidgetHostViewWin :
   virtual void WasHidden();
   virtual void SetSize(const gfx::Size& size);
   virtual HWND GetPluginHWND();
+  virtual void MovePluginWindows(
+      const std::vector<WebPluginGeometry>& plugin_window_moves);
   virtual void ForwardMouseEventToRenderer(UINT message,
                                            WPARAM wparam,
                                            LPARAM lparam);