Make dynamic_annotations build with -Wconstant-conversion from newer clangs.

third_party/libwebp/dsp/yuv_sse2.c

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the COPYING file in the root of the source
 // tree. An additional intellectual property rights grant can be found
 // in the file PATENTS. All contributing project authors may
 // be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // YUV->RGB conversion functions
@@ skipping 15 matching lines @@
 // B = (19077 * y + 33050 * u             - 17685) >> 6
 static void ConvertYUV444ToRGB(const __m128i* const Y0,
                                const __m128i* const U0,
                                const __m128i* const V0,
                                __m128i* const R,
                                __m128i* const G,
                                __m128i* const B) {
   const __m128i k19077 = _mm_set1_epi16(19077);
   const __m128i k26149 = _mm_set1_epi16(26149);
   const __m128i k14234 = _mm_set1_epi16(14234);
-  const __m128i k33050 = _mm_set1_epi16(33050);
+  // 33050 doesn't fit in a signed short: only use this with unsigned arithmetic
+  const __m128i k33050 = _mm_set1_epi16((short)33050);
   const __m128i k17685 = _mm_set1_epi16(17685);
   const __m128i k6419  = _mm_set1_epi16(6419);
   const __m128i k13320 = _mm_set1_epi16(13320);
   const __m128i k8708  = _mm_set1_epi16(8708);
 
   const __m128i Y1 = _mm_mulhi_epu16(*Y0, k19077);
 
   const __m128i R0 = _mm_mulhi_epu16(*V0, k26149);
   const __m128i R1 = _mm_sub_epi16(Y1, k14234);
   const __m128i R2 = _mm_add_epi16(R1, R0);
@@ skipping 718 matching lines @@
 
   WebPConvertRGBA32ToUV = ConvertRGBA32ToUV;
 }
 
 #else  // !WEBP_USE_SSE2
 
 WEBP_DSP_INIT_STUB(WebPInitSamplersSSE2)
 WEBP_DSP_INIT_STUB(WebPInitConvertARGBToYUVSSE2)
 
 #endif  // WEBP_USE_SSE2