Add VTSupport for dynamically linking VideoToolbox.

content/common/gpu/media/vt.sig

Index: content/common/gpu/media/vt.sig
diff --git a/content/common/gpu/media/vt.sig b/content/common/gpu/media/vt.sig
new file mode 100644
index 0000000000000000000000000000000000000000..06fa52f475e26c59a535e90ebaf1c42edce63787
--- /dev/null
+++ b/content/common/gpu/media/vt.sig
@@ -0,0 +1,14 @@
+//------------------------------------------------
+// Functions from CoreMedia.framework used in VTVideoDecodeAccelerator.
+//------------------------------------------------
+OSStatus CMBlockBufferCreateWithMemoryBlock(CFAllocatorRef structureAllocator, void *memoryBlock, size_t blockLength, CFAllocatorRef blockAllocator, const CMBlockBufferCustomBlockSource *customBlockSource, size_t offsetToData, size_t dataLength, CMBlockBufferFlags flags, CMBlockBufferRef *newBBufOut);
+OSStatus CMBlockBufferReplaceDataBytes(const void *sourceBytes, CMBlockBufferRef destinationBuffer, size_t offsetIntoDestination, size_t dataLength);
+OSStatus CMSampleBufferCreate(CFAllocatorRef allocator, CMBlockBufferRef dataBuffer, Boolean dataReady, CMSampleBufferMakeDataReadyCallback makeDataReadyCallback, void *makeDataReadyRefcon, CMFormatDescriptionRef formatDescription, CMItemCount numSamples, CMItemCount numSampleTimingEntries, const CMSampleTimingInfo *sampleTimingArray, CMItemCount numSampleSizeEntries, const size_t *sampleSizeArray, CMSampleBufferRef *sBufOut);
+OSStatus CMVideoFormatDescriptionCreateFromH264ParameterSets(CFAllocatorRef allocator, size_t parameterSetCount, const uint8_t *const *parameterSetPointers, const size_t *parameterSetSizes, int NALUnitHeaderLength, CMFormatDescriptionRef *formatDescriptionOut);
+CMVideoDimensions CMVideoFormatDescriptionGetDimensions(CMVideoFormatDescriptionRef videoDesc);
+
+//------------------------------------------------
+// Functions from VideoToolbox.framework used in VTVideoDecodeAccelerator.
+//------------------------------------------------
+OSStatus VTDecompressionSessionCreate(CFAllocatorRef allocator, CMVideoFormatDescriptionRef videoFormatDescription, CFDictionaryRef videoDecoderSpecification, CFDictionaryRef destinationImageBufferAttributes, const VTDecompressionOutputCallbackRecord *outputCallback, VTDecompressionSessionRef *decompressionSessionOut);
+OSStatus VTDecompressionSessionDecodeFrame(VTDecompressionSessionRef session, CMSampleBufferRef sampleBuffer, VTDecodeFrameFlags decodeFlags, void *sourceFrameRefCon, VTDecodeInfoFlags *infoFlagsOut);