Add support for loading pak files from arbitrary file regions.

base/files/memory_mapped_file.cc

Index: base/files/memory_mapped_file.cc
diff --git a/base/files/memory_mapped_file.cc b/base/files/memory_mapped_file.cc
index ace4e112628519137e7f56fbfb36f6176c2e8e83..e9656495844212d1fea11c16cabdca9118e1a540 100644
--- a/base/files/memory_mapped_file.cc
+++ b/base/files/memory_mapped_file.cc
@@ -6,9 +6,26 @@
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
+#include "base/sys_info.h"
 
 namespace base {
 
+const MemoryMappedFile::Region MemoryMappedFile::Region::kWholeFile;
+
+MemoryMappedFile::Region::Region() : offset(0), size(0) {
+}
+
+MemoryMappedFile::Region::Region(int64 offset, int64 size)
+    : offset(offset), size(size) {
+  DCHECK_GE(offset, 0);
+  DCHECK_GT(size, 0);
+}
+
+bool MemoryMappedFile::Region::operator==(
+    const MemoryMappedFile::Region& other) const {
+  return other.offset == offset && other.size == size;
+}
+
 MemoryMappedFile::~MemoryMappedFile() {
   CloseHandles();
 }
@@ -24,7 +41,7 @@ bool MemoryMappedFile::Initialize(const FilePath& file_name) {
     return false;
   }
 
-  if (!MapFileToMemory()) {
+  if (!MapFileRegionToMemory(Region::kWholeFile)) {
     CloseHandles();
     return false;
   }
@@ -33,12 +50,16 @@ bool MemoryMappedFile::Initialize(const FilePath& file_name) {
 }
 
 bool MemoryMappedFile::Initialize(File file) {
+  return Initialize(file.Pass(), Region::kWholeFile);
+}
+
+bool MemoryMappedFile::Initialize(File file, const Region& region) {
   if (IsValid())
     return false;
 
   file_ = file.Pass();
 
-  if (!MapFileToMemory()) {
+  if (!MapFileRegionToMemory(region)) {
     CloseHandles();
     return false;
   }
@@ -50,4 +71,18 @@ bool MemoryMappedFile::IsValid() const {
   return data_ != NULL;
 }
 
+// static
+void MemoryMappedFile::CalculateVMAlignedBoundaries(int64 start,
+                                                    int64 size,
+                                                    int64* aligned_start,
+                                                    int64* aligned_size,
+                                                    int32* offset) {
+  // Sadly, on Windows, the mmap alignment is not just equal to the page size.
+  const int64 mask = static_cast<int64>(SysInfo::VMAllocationGranularity()) - 1;
+  DCHECK_LT(mask, std::numeric_limits<int32>::max());
+  *offset = start & mask;
+  *aligned_start = start & ~mask;
+  *aligned_size = (size + *offset + mask) & ~mask;
+}
+
 }  // namespace base