Add wait function on GrContext to wait on semaphores.

This behaves like the SkSurface::wait call but is not tied to a specific
surface.

Change-Id: Ic572296e0f581204bf69a7178645d99e365c0692
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209648
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>

include/gpu/GrContext.h

@@ -242,6 +242,16 @@ public:
     ///////////////////////////////////////////////////////////////////////////
     // Misc.
 
+
+    /**
+     * Inserts a list of GPU semaphores that the current GPU-backed API must wait on before
+     * executing any more commands on the GPU. Skia will take ownership of the underlying semaphores
+     * and delete them once they have been signaled and waited on. If this call returns false, then
+     * the GPU back-end will not wait on any passed in semaphores, and the client will still own the
+     * semaphores.
+     */
+    bool wait(int numSemaphores, const GrBackendSemaphore* waitSemaphores);
+
     /**
      * Call to ensure all drawing to the context has been issued to the underlying 3D API.
      */

src/gpu/GrContext.cpp

@@ -239,6 +239,21 @@ int GrContext::maxSurfaceSampleCountForColorType(SkColorType colorType) const {
 
 ////////////////////////////////////////////////////////////////////////////////
 
+bool GrContext::wait(int numSemaphores, const GrBackendSemaphore waitSemaphores[]) {
+    if (!fGpu || fGpu->caps()->fenceSyncSupport()) {
+        return false;
+    }
+    for (int i = 0; i < numSemaphores; ++i) {
+        sk_sp<GrSemaphore> sema = fResourceProvider->wrapBackendSemaphore(
+                waitSemaphores[i], GrResourceProvider::SemaphoreWrapType::kWillWait,
+                kAdopt_GrWrapOwnership);
+        fGpu->waitSemaphore(std::move(sema));
+    }
+    return true;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
 GrSemaphoresSubmitted GrContext::flush(const GrFlushInfo& info) {
     ASSERT_SINGLE_OWNER
     if (this->abandoned()) {

src/gpu/GrRenderTargetContext.cpp

@@ -1774,7 +1774,6 @@ bool GrRenderTargetContext::waitOnSemaphores(int numSemaphores,
 
     auto resourceProvider = direct->priv().resourceProvider();
 
-    SkTArray<sk_sp<GrSemaphore>> semaphores(numSemaphores);
     for (int i = 0; i < numSemaphores; ++i) {
         sk_sp<GrSemaphore> sema = resourceProvider->wrapBackendSemaphore(
                 waitSemaphores[i], GrResourceProvider::SemaphoreWrapType::kWillWait,