Added SharedMemory::MapFrom.

base/shared_memory_posix.cc

Index: base/shared_memory_posix.cc
diff --git a/base/shared_memory_posix.cc b/base/shared_memory_posix.cc
index 7862f42c194fe2701293673efb6417bf2d7140a6..6209b4ee2b960cb626ef9b1f051508111e8ab8b0 100644
--- a/base/shared_memory_posix.cc
+++ b/base/shared_memory_posix.cc
@@ -16,6 +16,7 @@
 #include "base/threading/platform_thread.h"
 #include "base/safe_strerror_posix.h"
 #include "base/synchronization/lock.h"
+#include "base/sys_info.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 
@@ -219,7 +220,7 @@ bool SharedMemory::Open(const std::string& name, bool read_only) {
 
 #endif  // !defined(OS_ANDROID)
 
-bool SharedMemory::Map(size_t bytes) {
+bool SharedMemory::MapFrom(off_t offset, size_t bytes) {
   if (mapped_file_ == -1)
     return false;
 
@@ -242,8 +243,10 @@ bool SharedMemory::Map(size_t bytes) {
   }
 #endif
 
+  DCHECK_EQ(static_cast<size_t>(0),
+            offset & (SysInfo::VMAllocationGranularity() - 1));

[Mark Mentovai, 2013/01/15 21:51:42]

Is this really any of our business?

[Vitaly Buka (NO REVIEWS), 2013/01/15 22:13:05]

memory_ will be NULL, if value is not aligned. Just hit for developer to fix
calling code.

   memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
-                 MAP_SHARED, mapped_file_, 0);
+                 MAP_SHARED, mapped_file_, offset);
 
   bool mmap_succeeded = memory_ != (void*)-1 && memory_ != NULL;
   if (mmap_succeeded) {