Bug 1555653 Fix asserts in WindowBackBufferShm; r=stransky

Differential Revision: https://phabricator.services.mozilla.com/D33147

--HG--
extra : moz-landing-system : lando

widget/gtk/WindowSurfaceWayland.cpp

@@ -409,6 +409,7 @@ already_AddRefed<gfx::DrawTarget> WindowBackBufferShm::Lock() {
       mWaylandBuffer ? wl_proxy_get_id((struct wl_proxy*)mWaylandBuffer) : -1));
 
   gfx::IntSize lockSize(mWidth, mHeight);
+  mIsLocked = true;
   return gfxPlatform::CreateDrawTargetForData(
       static_cast<unsigned char*>(mShmPool.GetImageData()), lockSize,
       BUFFER_BPP * mWidth, GetSurfaceFormat());
@@ -593,9 +594,6 @@ WindowBackBuffer* WindowSurfaceWayland::GetWaylandBufferToDraw(
     return mWaylandBuffer;
   }
 
-  MOZ_ASSERT(!mPendingCommit,
-             "Uncommitted buffer switch, screen artifacts ahead.");
-
   // Front buffer is used by compositor, select a back buffer
   int availableBuffer;
   for (availableBuffer = 0; availableBuffer < BACK_BUFFER_NUM;

widget/gtk/WindowSurfaceWayland.h

@@ -44,8 +44,8 @@ class WaylandShmPool {
 class WindowBackBuffer {
  public:
   virtual already_AddRefed<gfx::DrawTarget> Lock() = 0;
-  virtual void Unlock(){};
-  virtual bool IsLocked() { return false; };
+  virtual void Unlock() = 0;
+  virtual bool IsLocked() = 0;
 
   void Attach(wl_surface* aSurface);
   virtual void Detach(wl_buffer* aBuffer) = 0;
@@ -89,9 +89,12 @@ class WindowBackBufferShm : public WindowBackBuffer {
   ~WindowBackBufferShm();
 
   already_AddRefed<gfx::DrawTarget> Lock();
+  bool IsLocked() { return mIsLocked; };
+  void Unlock() { mIsLocked = false; };
 
   void Detach(wl_buffer* aBuffer);
   bool IsAttached() { return mAttached; }
+  void SetAttached() { mAttached = true; };
 
   void Clear();
   bool Resize(int aWidth, int aHeight);
@@ -101,7 +104,6 @@ class WindowBackBufferShm : public WindowBackBuffer {
   int GetHeight() { return mHeight; };
 
   wl_buffer* GetWlBuffer() { return mWaylandBuffer; };
-  void SetAttached() { mAttached = true; };
 
  private:
   void Create(int aWidth, int aHeight);
@@ -116,6 +118,7 @@ class WindowBackBufferShm : public WindowBackBuffer {
   int mWidth;
   int mHeight;
   bool mAttached;
+  bool mIsLocked;
 };
 
 #ifdef HAVE_LIBDRM