Speed up IdAllocator.

gpu/command_buffer/common/id_allocator_test.cc

Index: gpu/command_buffer/common/id_allocator_test.cc
===================================================================
--- gpu/command_buffer/common/id_allocator_test.cc	(revision 86796)
+++ gpu/command_buffer/common/id_allocator_test.cc	(working copy)
@@ -49,6 +49,9 @@
 TEST_F(IdAllocatorTest, TestAdvanced) {
   IdAllocator *allocator = id_allocator();
 
+  // Allocate the highest possible ID, to make life awkward.
+  allocator->AllocateIDAtOrAbove(-1);
+
   // Allocate a significant number of resources.
   const unsigned int kNumResources = 100;
   ResourceId ids[kNumResources];
@@ -95,4 +98,16 @@
   EXPECT_GT(id3, kOffset);
 }
 
+// Checks that AllocateIdAtOrAbove wraps around at the maximum 32-bit value.
+TEST_F(IdAllocatorTest, AllocateIdAtOrAboveWrapsAround) {
+  const ResourceId kMaxPossibleOffset = -1;
+  IdAllocator* allocator = id_allocator();
+  ResourceId id1 = allocator->AllocateIDAtOrAbove(kMaxPossibleOffset);
+  EXPECT_EQ(kMaxPossibleOffset, id1);
+  ResourceId id2 = allocator->AllocateIDAtOrAbove(kMaxPossibleOffset);
+  EXPECT_EQ(1u, id2);
+  ResourceId id3 = allocator->AllocateIDAtOrAbove(kMaxPossibleOffset);
+  EXPECT_EQ(2u, id3);
+}
+
 }  // namespace gpu