Update libwebp to 0.4.0

third_party/libwebp/utils/thread.h

Index: third_party/libwebp/utils/thread.h
diff --git a/third_party/libwebp/utils/thread.h b/third_party/libwebp/utils/thread.h
index 13a61a4c84194c3374080cbf03d881d3cd6af40d..aef33bdaf21f18fe896485e4818b1e851bb10b52 100644
--- a/third_party/libwebp/utils/thread.h
+++ b/third_party/libwebp/utils/thread.h
@@ -18,11 +18,11 @@
 #include "config.h"
 #endif
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
-#if WEBP_USE_THREAD
+#ifdef WEBP_USE_THREAD
 
 #if defined(_WIN32)
 
@@ -55,7 +55,7 @@ typedef int (*WebPWorkerHook)(void*, void*);
 
 // Synchronize object used to launch job in the worker thread
 typedef struct {
-#if WEBP_USE_THREAD
+#ifdef WEBP_USE_THREAD
   pthread_mutex_t mutex_;
   pthread_cond_t  condition_;
   pthread_t       thread_;
@@ -79,13 +79,18 @@ int WebPWorkerSync(WebPWorker* const worker);
 // hook/data1/data2 can be changed at any time before calling this function,
 // but not be changed afterward until the next call to WebPWorkerSync().
 void WebPWorkerLaunch(WebPWorker* const worker);
+// This function is similar to WebPWorkerLaunch() except that it calls the
+// hook directly instead of using a thread. Convenient to bypass the thread
+// mechanism while still using the WebPWorker structs. WebPWorkerSync() must
+// still be called afterward (for error reporting).
+void WebPWorkerExecute(WebPWorker* const worker);
 // Kill the thread and terminate the object. To use the object again, one
 // must call WebPWorkerReset() again.
 void WebPWorkerEnd(WebPWorker* const worker);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif