Bug 1369724: Fix setting size for fake H264 codec r=jya

From bug 1341285

MozReview-Commit-ID: E6g6phiQC5H

dom/media/gmp-plugin-openh264/gmp-fake-openh264.cpp

@@ -205,7 +205,8 @@ class FakeVideoEncoder : public GMPVideoEncoder {
     }
     memcpy(f->Buffer(), &eframe, sizeof(eframe));
     if (frame_type  == kGMPKeyFrame) {
-      *((uint32_t*) f->Buffer() + sizeof(eframe)) = BIG_FRAME;
+      // set the size for the fake iframe
+      *((uint32_t*) (f->Buffer() + sizeof(eframe))) = BIG_FRAME;
     }
 
     f->SetEncodedWidth (inputImage->Width());

media/webrtc/signaling/src/media-conduit/WebrtcGmpVideoCodec.cpp

@@ -591,11 +591,12 @@ WebrtcGmpVideoEncoder::Encoded(GMPVideoEncodedFrame* aEncodedFrame,
         default:
           MOZ_CRASH("GMP_BufferType already handled in switch above");
       }
-      if (buffer+size > end) {
+      MOZ_ASSERT(size != 0 &&
+                 buffer+size <= end); // in non-debug code, don't crash in this case
+      if (size == 0 || buffer+size > end) {
         // XXX see above - should we kill the plugin for returning extra bytes?  Probably
         LOG(LogLevel::Error,
-            ("GMP plugin returned badly formatted encoded data: end is %td bytes past buffer end",
-             buffer+size - end));
+            ("GMP plugin returned badly formatted encoded data: buffer=%p, size=%d, end=%p", buffer, size, end));
         return;
       }
       // XXX optimize by making buffer an offset