bug 755070 - Scrolling causes after paint notifications which causes screenshotting which causes checkerboarding, screenshot only on idle r=kats

--HG--
extra : rebase_source : be056e08b6a7d8aa339b12cbeb58d42054f5a118

ipc/chromium/src/base/message_loop.cc

@@ -256,6 +256,14 @@ void MessageLoop::PostNonNestableDelayedTask(
   PostTask_Helper(from_here, task, delay_ms, false);
 }
 
+void MessageLoop::PostIdleTask(
+    const tracked_objects::Location& from_here, Task* task) {
+  DCHECK(current() == this);
+  task->SetBirthPlace(from_here);
+  PendingTask pending_task(task, false);
+  deferred_non_nestable_work_queue_.push(pending_task);
+}
+
 // Possibly called on a background thread!
 void MessageLoop::PostTask_Helper(
     const tracked_objects::Location& from_here, Task* task, int delay_ms,

ipc/chromium/src/base/message_loop.h

@@ -121,6 +121,10 @@ public:
   void PostNonNestableDelayedTask(
       const tracked_objects::Location& from_here, Task* task, int delay_ms);
 
+  // PostIdleTask is not thread safe and should be called on this thread
+  void PostIdleTask(
+      const tracked_objects::Location& from_here, Task* task);
+
   // A variant on PostTask that deletes the given object.  This is useful
   // if the object needs to live until the next run of the MessageLoop (for
   // example, deleting a RenderProcessHost from within an IPC callback is not

widget/android/nsAppShell.cpp

@@ -6,6 +6,8 @@
 // Make sure the order of included headers
 #include "base/basictypes.h"
 #include "nspr/prtypes.h"
+#include "base/message_loop.h"
+#include "base/task.h"
 
 #include "mozilla/Hal.h"
 #include "nsAppShell.h"
@@ -63,6 +65,34 @@ nsAppShell *nsAppShell::gAppShell = nsnull;
 
 NS_IMPL_ISUPPORTS_INHERITED1(nsAppShell, nsBaseAppShell, nsIObserver)
 
+class ScreenshotRunnable : public nsRunnable {
+public:
+    ScreenshotRunnable(nsIAndroidBrowserApp* aBrowserApp, int aTabId, nsTArray<nsIntPoint>& aPoints, int aToken):
+        mBrowserApp(aBrowserApp), mTabId(aTabId), mPoints(aPoints), mToken(aToken) {}
+
+    virtual nsresult Run() {
+        nsCOMPtr<nsIDOMWindow> domWindow;
+        nsCOMPtr<nsIBrowserTab> tab;
+        mBrowserApp->GetBrowserTab(mTabId, getter_AddRefs(tab));
+        if (!tab)
+            return NS_OK;
+
+        tab->GetWindow(getter_AddRefs(domWindow));
+        if (!domWindow)
+            return NS_OK;
+
+        float scale = 1.0;
+        NS_ASSERTION(mPoints.Length() == 4, "Screenshot event does not have enough coordinates");
+
+        AndroidBridge::Bridge()->TakeScreenshot(domWindow, mPoints[0].x, mPoints[0].y, mPoints[1].x, mPoints[1].y, mPoints[3].x, mPoints[3].y, mTabId, scale, mToken);
+        return NS_OK;
+    }
+private:
+    nsCOMPtr<nsIAndroidBrowserApp> mBrowserApp;
+    nsTArray<nsIntPoint> mPoints;
+    int mTabId, mToken;
+};
+
 class AfterPaintListener : public nsIDOMEventListener {
   public:
     NS_DECL_ISUPPORTS
@@ -425,21 +455,12 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
             break;
 
         PRInt32 token = curEvent->Flags();
-
-        nsCOMPtr<nsIDOMWindow> domWindow;
-        nsCOMPtr<nsIBrowserTab> tab;
-        mBrowserApp->GetBrowserTab(curEvent->MetaState(), getter_AddRefs(tab));
-        if (!tab)
-            break;
-
-        tab->GetWindow(getter_AddRefs(domWindow));
-        if (!domWindow)
-            break;
-
-        float scale = 1.0;
+        PRInt32 tabId = curEvent->MetaState();
         nsTArray<nsIntPoint> points = curEvent->Points();
-        NS_ASSERTION(points.Length() == 4, "Screenshot event does not have enough coordinates");
-        bridge->TakeScreenshot(domWindow, points[0].x, points[0].y, points[1].x, points[1].y, points[3].x, points[3].y, curEvent->MetaState(), scale, curEvent->Flags());
+        nsCOMPtr<ScreenshotRunnable> sr = 
+            new ScreenshotRunnable(mBrowserApp, tabId, points, token);
+        MessageLoop::current()->PostIdleTask(
+            FROM_HERE, NewRunnableMethod(sr.get(), &ScreenshotRunnable::Run));
         break;
     }