import changes from `devel' branch of rmottola/Arctic-Fox:

- Bug 943820 - Add visibleLabel attribute/property and tests. r=ttaubert (95540e489)
- Bug 902729 - Add a new telemetry probe for session lifetimes. r=ttaubert (725e51e1a)
- Bug 1150529 - Remove code for expired telemetry histograms r=Yoric (6a1540c7f)
- Bug 732303 - Redesign safe mode dialog with the profile reset option. r=dolske, ui-r=limi (8a0253b18)
- Bug 894188 - "resetSupported is not defined" in safe mode dialog. r=jaws (a45930696)
- Bug 498181 - Offer to reset a user's profile if it was last used more than two months ago. r=jaws (5295b1629)
- fix duplicted entries (eb068619a)
- Bug 1063702 - Update all Reset Firefox strings and relevant UI to new UX requirements. r=MattN (4771a9da5)
- remove some DEVTOOLS and console related code, not found in FF/TFF (11b163829)
- Bug 1147236 - Use AppConstants in session store code (r=ttaubert) (68b6ceedf)
- fix redeclaration of cc (b1b1611b0)
- bug 1137792 - Ignore the first timing for an add-on r=mossop (59e48d895)
- Bug 1140113 - Catch direct (and some indirect) callers of CreateDrawTarget* and deal with failure. r=mstange (89cf1d361)
- Bug 1010552 - Breakpoints not removed from server when tab is closed;r=jlong (bf63d0b31)
- Bug 1139181 - Add missing MIRTypes to StringFromMIRType(). r=efaust (d716f2fe9)
- Bug 950373 part.2 Don't consume keys which are used by <tree> for navigation in session restore UI r=enndeakin (06435f06b)
- Bug 925771 - Generate consecutive window IDs to avoid collisions. r=ttaubert (74c81ef33)
- Bug 931891 - [Australis] Backed out bug 887515 and the followups (bug 896291, 909662, 896896). r=ttaubert (b8f02497e)
- Bug 930901 - Move TabState and TabAttributes to their own JSMs r=billm (be255adac)

gfx/layers/client/TextureClient.cpp

@@ -544,7 +544,17 @@ bool TextureClient::CopyToTextureClient(TextureClient* aTarget,
   }
 
   RefPtr<DrawTarget> destinationTarget = aTarget->BorrowDrawTarget();
+  if (!destinationTarget) {
+      gfxWarning() << "TextureClient::CopyToTextureClient (dest) failed in BorrowDrawTarget";
+    return false;
+  }
+
   RefPtr<DrawTarget> sourceTarget = BorrowDrawTarget();
+  if (!sourceTarget) {
+    gfxWarning() << "TextureClient::CopyToTextureClient (src) failed in BorrowDrawTarget";
+    return false;
+  }
+
   RefPtr<gfx::SourceSurface> source = sourceTarget->Snapshot();
   destinationTarget->CopySurface(source,
                                  aRect ? *aRect : gfx::IntRect(gfx::IntPoint(0, 0), GetSize()),