VirtualDisplaySurface propagate reallocation to VDS producer

When dequeuing from the source through refreshOutputBuffer(),
the dequeue result, BUFFER_NEEDS_REALLOCATION, is not propagated back up.
RenderSurface will not reallocate from VirtualDisplaySurface
 in this situation, causing GLES to render to the wrong buffer.

Wrong buffer example,
beginFrame() -> refreshOutputBuffer() -> dequeueBuffer()
-> dequeueBuffer() needs reallocation.
but the result in refreshOuputBuffer() is overwritten by
mHwc.setOutputBuffer().
(the result is also not received by VDS itself)

We need a flag to indicate producer slot need reallocation,
so that we can sent reallocation to Consumer.

Bug: 157204337
Test: simulate second display with debug.sf.enable_hwc_vds = 1
Change-Id: Ibcbc3bd1ef857382ea9882dd10e0bd55759406f4
diff --git a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
index fba3261..c8cd442 100644
--- a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
+++ b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
@@ -73,6 +73,7 @@
         mOutputUsage(GRALLOC_USAGE_HW_COMPOSER),
         mProducerSlotSource(0),
         mProducerBuffers(),
+        mProducerSlotNeedReallocation(0),
         mQueueBufferOutput(),
         mSinkBufferWidth(0),
         mSinkBufferHeight(0),
@@ -335,10 +336,14 @@
             dbgSourceStr(source), *sslot, pslot, result);
     uint64_t sourceBit = static_cast<uint64_t>(source) << pslot;
 
+    // reset producer slot reallocation flag
+    mProducerSlotNeedReallocation &= ~(1ULL << pslot);
+
     if ((mProducerSlotSource & (1ULL << pslot)) != sourceBit) {
         // This slot was previously dequeued from the other source; must
         // re-request the buffer.
-        result |= BUFFER_NEEDS_REALLOCATION;
+        mProducerSlotNeedReallocation |= 1ULL << pslot;
+
         mProducerSlotSource &= ~(1ULL << pslot);
         mProducerSlotSource |= sourceBit;
     }
@@ -360,6 +365,9 @@
                 dbgSourceStr(source), pslot, mProducerBuffers[pslot].get(),
                 mProducerBuffers[pslot]->getPixelFormat(),
                 mProducerBuffers[pslot]->getUsage());
+
+        // propagate reallocation to VDS consumer
+        mProducerSlotNeedReallocation |= 1ULL << pslot;
     }
 
     return result;
@@ -434,6 +442,11 @@
     if (outBufferAge) {
         *outBufferAge = 0;
     }
+
+    if ((mProducerSlotNeedReallocation & (1ULL << *pslot)) != 0) {
+        result |= BUFFER_NEEDS_REALLOCATION;
+    }
+
     return result;
 }