libwebp: update to 0.4.2-rc2

third_party/libwebp/dsp/dsp.h

Index: third_party/libwebp/dsp/dsp.h
diff --git a/third_party/libwebp/dsp/dsp.h b/third_party/libwebp/dsp/dsp.h
index f8813d774dde9efe48f98b4e99e5ce47b523fd20..52c44b2dc18323e8265abf49340ff71f032c7491 100644
--- a/third_party/libwebp/dsp/dsp.h
+++ b/third_party/libwebp/dsp/dsp.h
@@ -32,9 +32,19 @@ extern "C" {
 # define LOCAL_GCC_PREREQ(maj, min) \
     (LOCAL_GCC_VERSION >= (((maj) << 8) | (min)))
 #else
+# define LOCAL_GCC_VERSION 0
 # define LOCAL_GCC_PREREQ(maj, min) 0
 #endif
 
+#ifdef __clang__
+# define LOCAL_CLANG_VERSION ((__clang_major__ << 8) | __clang_minor__)
+# define LOCAL_CLANG_PREREQ(maj, min) \
+    (LOCAL_CLANG_VERSION >= (((maj) << 8) | (min)))
+#else
+# define LOCAL_CLANG_VERSION 0
+# define LOCAL_CLANG_PREREQ(maj, min) 0
+#endif  // __clang__
+
 #if defined(_MSC_VER) && _MSC_VER > 1310 && \
     (defined(_M_X64) || defined(_M_IX86))
 #define WEBP_MSC_SSE2  // Visual C++ SSE2 targets
@@ -62,6 +72,9 @@ extern "C" {
 
 #if defined(__mips__) && !defined(__mips64) && (__mips_isa_rev < 6)
 #define WEBP_USE_MIPS32
+#if (__mips_isa_rev >= 2)
+#define WEBP_USE_MIPS32_R2
+#endif
 #endif
 
 typedef enum {
@@ -244,6 +257,13 @@ extern void (*WebPApplyAlphaMultiply)(
 extern void (*WebPApplyAlphaMultiply4444)(
     uint8_t* rgba4444, int w, int h, int stride);
 
+// Extract the alpha values from 32b values in argb[] and pack them into alpha[]
+// (this is the opposite of WebPDispatchAlpha).
+// Returns true if there's only trivial 0xff alpha values.
+extern int (*WebPExtractAlpha)(const uint8_t* argb, int argb_stride,
+                               int width, int height,
+                               uint8_t* alpha, int alpha_stride);
+
 // Pre-Multiply operation transforms x into x * A / 255  (where x=Y,R,G or B).
 // Un-Multiply operation transforms x into x * 255 / A.