Surface synchronization: Accept update from parent if embed token changed

The ChildLocalSurfaceIdAllocator should accept updates from the parent if
the embed token changed. This can happen if an iframe performs a cross-process
navigation.

Bug: 672962
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel
Change-Id: I1f78a39d787bc7cf43b13e2092f4b5974eace954
Reviewed-on: https://chromium-review.googlesource.com/1096104Reviewed-by: Saman Sami <samans@chromium.org>
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566436}

components/viz/common/surfaces/child_local_surface_id_allocator.cc

@@ -17,8 +17,10 @@ ChildLocalSurfaceIdAllocator::ChildLocalSurfaceIdAllocator()
 
 bool ChildLocalSurfaceIdAllocator::UpdateFromParent(
     const LocalSurfaceId& parent_allocated_local_surface_id) {
-  if (parent_allocated_local_surface_id.parent_sequence_number() >
-      current_local_surface_id_.parent_sequence_number()) {
+  if ((parent_allocated_local_surface_id.parent_sequence_number() >
+       current_local_surface_id_.parent_sequence_number()) ||
+      parent_allocated_local_surface_id.embed_token() !=
+          current_local_surface_id_.embed_token()) {
     current_local_surface_id_.parent_sequence_number_ =
         parent_allocated_local_surface_id.parent_sequence_number_;
     current_local_surface_id_.embed_token_ =

components/viz/common/surfaces/child_local_surface_id_allocator_unittest.cc

@@ -4,6 +4,7 @@
 
 #include "components/viz/common/surfaces/child_local_surface_id_allocator.h"
 
+#include "components/viz/common/surfaces/parent_local_surface_id_allocator.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 // ChildLocalSurfaceIdAllocator has 1 accessor which does not alter state:
@@ -105,6 +106,26 @@ TEST(ChildLocalSurfaceIdAllocatorTest,
             parent_allocated_local_surface_id.embed_token());
 }
 
+// UpdateFromParent() on a child allocator should accept the parent's
+// LocalSurfaceId if only the embed_token changed.
+TEST(ChildLocalSurfaceIdAllocatorTest, UpdateFromParentEmbedTokenChanged) {
+  ParentLocalSurfaceIdAllocator parent_allocator;
+  ParentLocalSurfaceIdAllocator parent_allocator2;
+  ChildLocalSurfaceIdAllocator child_allocator;
+
+  EXPECT_TRUE(parent_allocator.GenerateId().is_valid());
+  EXPECT_TRUE(child_allocator.UpdateFromParent(
+      parent_allocator.GetCurrentLocalSurfaceId()));
+  EXPECT_LE(
+      parent_allocator2.GetCurrentLocalSurfaceId().parent_sequence_number(),
+      parent_allocator.GetCurrentLocalSurfaceId().parent_sequence_number());
+  EXPECT_NE(parent_allocator2.GetCurrentLocalSurfaceId().embed_token(),
+            parent_allocator.GetCurrentLocalSurfaceId().embed_token());
+
+  EXPECT_TRUE(child_allocator.UpdateFromParent(
+      parent_allocator2.GetCurrentLocalSurfaceId()));
+}
+
 // GenerateId() on a child allocator should monotonically increment the child
 // sequence number.
 TEST(ChildLocalSurfaceIdAllocatorTest,