Remove CHECK that verifies that |frame| was created

As there are only a few crashes from this CHECK, removing it. It appears
that the crash happens due to the SharedBufferHandle not being able to be
mapped into the current address space. Since this happens so infrequently,
simply return a NULL frame and let upstream handle the error.

BUG=829443
TEST=media_mojo_unittests pass

Change-Id: I645839d1975e9ec0629fe4ff29b91db8c52bf44b
Reviewed-on: https://chromium-review.googlesource.com/1114346Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570559}

media/mojo/services/mojo_cdm_allocator.cc

@@ -149,13 +149,10 @@ class MojoCdmVideoFrame : public VideoFrameImpl {
             Stride(kYPlane), Stride(kUPlane), Stride(kVPlane),
             base::TimeDelta::FromMicroseconds(Timestamp()));
 
-    // If |frame| is not created something is wrong with the video frame data
-    // returned by the CDM. Catch it here rather than returning a null frame
-    // to the renderer.
-    // TODO(crbug.com/829443). Monitor crashes to see if this happens.
-    CHECK(frame);
-
-    frame->SetMojoSharedBufferDoneCB(mojo_shared_buffer_done_cb_);
+    // |frame| could fail to be created if the memory can't be mapped into
+    // this address space.
+    if (frame)
+      frame->SetMojoSharedBufferDoneCB(mojo_shared_buffer_done_cb_);
     return frame;
   }