This fixes http://b/issue?id=1257424, which is a need to implement a global backing store cache. The current backing store cache is only used for invisible tabs and every other RenderWidgetHost holds a reference to its backing store.

This CB proposes a change where in we have a global backing store cache, whose size can be controlled based on strategies like available resources etc. At this point the strategy is not implemented and the size is left at 5.
We no longer maintain a reference to the backing store in the RenderWidgetHost. Every host queries the global cache for its backing store. The cache provides methods to create the backing store and populate it with the required dib. 
The other change is to use the renderer dib when the size of the bitmap being painted is the same as the backing store size. This is an attempt to improve performance in operations like scrolling. 

Bug=1257424





git-svn-id: svn://svn.chromium.org/chrome/trunk/src@422 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 33 insertions, 11 deletions

diff --git a/chrome/renderer/render_process.h b/chrome/renderer/render_process.h
index 49f43e2..9ecbb13 100644
--- a/chrome/renderer/render_process.h
+++ b/chrome/renderer/render_process.h
@@ -63,6 +63,9 @@ class RenderProcess : public ChildProcess {
   // this function to free the SharedMemory object.
   static void FreeSharedMemory(SharedMemory* mem);
 
+  // Deletes the shared memory allocated by AllocSharedMemory.
+  static void DeleteSharedMem(SharedMemory* mem);
+
  private:
   friend class ChildProcessFactory<RenderProcess>;
   RenderProcess(const std::wstring& channel_name);
@@ -83,10 +86,6 @@ class RenderProcess : public ChildProcess {
 
   static ChildProcess* ClassFactory(const std::wstring& channel_name);
 
-  // This is here so consumers will use FreeSharedMemory instead.  A destructor
-  // on SharedMemory would be too tempting.
-  static void DeleteSharedMem(SharedMemory* mem);
-
   // Look in the shared memory cache for a suitable object to reuse.  Returns
   // NULL if there is none.
   SharedMemory* GetSharedMemFromCache(size_t size);
diff --git a/chrome/renderer/render_widget.cc b/chrome/renderer/render_widget.cc
index c5db805..2560438 100644
--- a/chrome/renderer/render_widget.cc
+++ b/chrome/renderer/render_widget.cc
@@ -182,6 +182,7 @@ IPC_DEFINE_MESSAGE_MAP(RenderWidget)
   IPC_MESSAGE_HANDLER(ViewMsg_SetFocus, OnSetFocus)
   IPC_MESSAGE_HANDLER(ViewMsg_ImeSetInputMode, OnImeSetInputMode)
   IPC_MESSAGE_HANDLER(ViewMsg_ImeSetComposition, OnImeSetComposition)
+  IPC_MESSAGE_HANDLER(ViewMsg_Repaint, OnMsgRepaint)
   IPC_MESSAGE_UNHANDLED_ERROR()
 IPC_END_MESSAGE_MAP()
 
@@ -295,17 +296,24 @@ void RenderWidget::OnWasRestored(bool needs_repainting) {
   DidInvalidateRect(webwidget_, gfx::Rect(size_.width(), size_.height()));
 }
 
-void RenderWidget::OnPaintRectAck() {
+void RenderWidget::OnPaintRectAck(bool drop_bitmap) {
   DCHECK(paint_reply_pending());
   paint_reply_pending_ = false;
 
-  // If we sent a PaintRect message with a zero-sized bitmap, then
-  // we should have no current paint buf.
-  if (current_paint_buf_) {
-    RenderProcess::FreeSharedMemory(current_paint_buf_);
-    current_paint_buf_ = NULL;
+  if (drop_bitmap) {
+    if (current_paint_buf_) {
+      RenderProcess::DeleteSharedMem(current_paint_buf_);
+    }
+  } else {
+    // If we sent a PaintRect message with a zero-sized bitmap, then
+    // we should have no current paint buf.
+    if (current_paint_buf_) {
+      RenderProcess::FreeSharedMemory(current_paint_buf_);
+    }
   }
 
+  current_paint_buf_ = NULL;
+
   // Continue painting if necessary...
   DoDeferredPaint();
 }
@@ -691,6 +699,16 @@ void RenderWidget::OnImeSetComposition(int string_type,
   }
 }
 
+void RenderWidget::OnMsgRepaint(const gfx::Size& size_to_paint) {
+  // During shutdown we can just ignore this message.
+  if (!webwidget_)
+    return;
+
+  set_next_paint_is_repaint_ack();
+  gfx::Rect repaint_rect(size_to_paint.width(), size_to_paint.height());
+  DidInvalidateRect(webwidget_, repaint_rect);
+}
+
 void RenderWidget::UpdateIME() {
   // If a browser process does not have IMEs, its IMEs are not active, or there
   // are not any attached widgets.
diff --git a/chrome/renderer/render_widget.h b/chrome/renderer/render_widget.h
index 720df07..48b40ee 100644
--- a/chrome/renderer/render_widget.h
+++ b/chrome/renderer/render_widget.h
@@ -133,7 +133,7 @@ class RenderWidget : public IPC::Channel::Listener,
   void OnResize(const gfx::Size& new_size);
   void OnWasHidden();
   void OnWasRestored(bool needs_repainting);
-  void OnPaintRectAck();
+  void OnPaintRectAck(bool drop_bitmap);
   void OnScrollRectAck();
   void OnHandleInputEvent(const IPC::Message& message);
   void OnMouseCaptureLost();
@@ -142,6 +142,7 @@ class RenderWidget : public IPC::Channel::Listener,
   void OnImeSetComposition(int string_type, int cursor_position,
                            int target_start, int target_end,
                            const std::wstring& ime_string);
+  void OnMsgRepaint(const gfx::Size& size_to_paint);
 
   // True if a PaintRect_ACK message is pending.
   bool paint_reply_pending() const {
@@ -169,6 +170,10 @@ class RenderWidget : public IPC::Channel::Listener,
     next_paint_flags_ |= ViewHostMsg_PaintRect_Flags::IS_RESTORE_ACK;
   }
 
+  void set_next_paint_is_repaint_ack() {
+    next_paint_flags_ |= ViewHostMsg_PaintRect_Flags::IS_REPAINT_ACK;
+  }
+
   // Called when a renderer process moves an input focus or updates the
   // position of its caret.
   // This function compares them with the previous values, and send them to