Added SharedMemory::MapFrom.

base/shared_memory_unittest.cc

Index: base/shared_memory_unittest.cc
diff --git a/base/shared_memory_unittest.cc b/base/shared_memory_unittest.cc
index bd537692f4880febe1ce12dc9a18e91991296ca4..f02e2753130fafc3f1bde74351b099482f0b2b8c 100644
--- a/base/shared_memory_unittest.cc
+++ b/base/shared_memory_unittest.cc
@@ -8,6 +8,7 @@
 #endif
 #include "base/memory/scoped_ptr.h"
 #include "base/shared_memory.h"
+#include "base/sys_info.h"
 #include "base/test/multiprocess_test.h"
 #include "base/threading/platform_thread.h"
 #include "base/time.h"
@@ -343,6 +344,33 @@ TEST(SharedMemoryTest, AnonymousPrivate) {
   }
 }
 
+TEST(SharedMemoryTest, MapAt) {
+  ASSERT_TRUE(SysInfo::VMAllocationGranularity() >= sizeof(uint32));
+  const size_t kCount = SysInfo::VMAllocationGranularity();
+  const size_t kDataSize = kCount * sizeof(uint32);
+
+  SharedMemory memory;
+  ASSERT_TRUE(memory.CreateAndMapAnonymous(kDataSize));
+  ASSERT_TRUE(memory.Map(kDataSize));
+  uint32* ptr = static_cast<uint32*>(memory.memory());
+  ASSERT_NE(ptr, static_cast<void*>(NULL));
+
+  for (size_t i = 0; i < kCount; ++i) {
+    ptr[i] = i;
+  }
+
+  memory.Unmap();
+
+  off_t offset = SysInfo::VMAllocationGranularity();
+  ASSERT_TRUE(memory.MapAt(offset, kDataSize - offset));
+  offset /= sizeof(uint32);
+  ptr = static_cast<uint32*>(memory.memory());
+  ASSERT_NE(ptr, static_cast<void*>(NULL));
+  for (size_t i = offset; i < kCount; ++i) {
+    EXPECT_EQ(ptr[i - offset], i);
+  }
+}
+
 #if defined(OS_POSIX)
 // Create a shared memory object, mmap it, and mprotect it to PROT_EXEC.
 TEST(SharedMemoryTest, AnonymousExecutable) {