After a create-on-bind, the subsequent glGen* should not waste handle space.

Consider this calling sequence:
glBindTexture(GL_TEXTURE_2D, 3); // create-on-bind
glGenTextures(1, tex);

Before this fix, mUnallocatedList in HandleAllocator is in reverse sorted
order. It's split into (4, MAX_UINT) and (1, 3). The glGen gets tex = 4,
and handles 1 and 2 will not be allocated until it reaches MAX_UINT.
With this fix, the elements in mUnallocatedList is in sorted order
(1, 3) and (4, MAX_UINT). So tex is 1, and we can have all rest handles.

Change-Id: If408ea92f7c243791119fe386e3e0ea27954e55c
Reviewed-on: https://chromium-review.googlesource.com/273886
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Minmin Gong <mgong@microsoft.com>

src/libANGLE/HandleAllocator.cpp

@@ -20,7 +20,7 @@ struct HandleAllocator::HandleRangeComparator
 {
     bool operator()(const HandleRange &range, GLuint handle) const
     {
-        return (handle < range.begin);
+        return (range.end < handle);
     }
 };
 
@@ -120,13 +120,13 @@ void HandleAllocator::reserve(GLuint handle)
     // need to split the range
     auto placementIt = mUnallocatedList.erase(boundIt);
 
-    if (begin != handle)
-    {
-        placementIt = mUnallocatedList.insert(placementIt, HandleRange(begin, handle));
-    }
     if (handle + 1 != end)
     {
-        mUnallocatedList.insert(placementIt, HandleRange(handle + 1, end));
+        placementIt = mUnallocatedList.insert(placementIt, HandleRange(handle + 1, end));
+    }
+    if (begin != handle)
+    {
+        mUnallocatedList.insert(placementIt, HandleRange(begin, handle));
     }
 }
 

src/libANGLE/HandleAllocator_unittest.cpp

@@ -103,4 +103,24 @@ TEST(HandleAllocatorTest, ReserveMaxUintHandle)
     EXPECT_EQ(1u, normalHandle);
 }
 
+// To test if the allocator keep the handle in a sorted order.
+TEST(HandleAllocatorTest, SortedOrderHandle)
+{
+    gl::HandleAllocator allocator;
+
+    allocator.reserve(3);
+
+    GLuint allocatedList[5];
+    for (GLuint count = 0; count < 5; count++)
+    {
+        allocatedList[count] = allocator.allocate();
+    }
+
+    EXPECT_EQ(1u, allocatedList[0]);
+    EXPECT_EQ(2u, allocatedList[1]);
+    EXPECT_EQ(4u, allocatedList[2]);
+    EXPECT_EQ(5u, allocatedList[3]);
+    EXPECT_EQ(6u, allocatedList[4]);
+}
+
 }