Revert 257300 "Disallow calling Map on currently-mapped SharedMe..."

Crashes PrintWebViewHelperTests.

> Disallow calling Map on currently-mapped SharedMemory
> 
> This would leak the previous mapping of the memory.
> 
> BUG=
> 
> Review URL: https://codereview.chromium.org/195893022

TBR=jbauman@chromium.org

Review URL: https://codereview.chromium.org/200623007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257311 0039d316-1c4b-4281-b951-d872f2087c98

5 files changed, 2 insertions, 24 deletions

diff --git a/base/memory/shared_memory.h b/base/memory/shared_memory.h
index 27c3747..8e32e72 100644
--- a/base/memory/shared_memory.h
+++ b/base/memory/shared_memory.h
@@ -154,8 +154,7 @@ class BASE_EXPORT SharedMemory {
   // Maps the shared memory into the caller's address space.
   // Returns true on success, false otherwise.  The memory address
   // is accessed via the memory() accessor.  The mapped address is guaranteed to
-  // have an alignment of at least MAP_MINIMUM_ALIGNMENT. This method will fail
-  // if this object is currently mapped.
+  // have an alignment of at least MAP_MINIMUM_ALIGNMENT.
   bool Map(size_t bytes) {
     return MapAt(0, bytes);
   }
diff --git a/base/memory/shared_memory_nacl.cc b/base/memory/shared_memory_nacl.cc
index 39625ee..7647400 100644
--- a/base/memory/shared_memory_nacl.cc
+++ b/base/memory/shared_memory_nacl.cc
@@ -91,9 +91,6 @@ bool SharedMemory::MapAt(off_t offset, size_t bytes) {
   if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
     return false;
 
-  if (memory_)
-    return false;
-
   memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
                  MAP_SHARED, mapped_file_, offset);
 
diff --git a/base/memory/shared_memory_posix.cc b/base/memory/shared_memory_posix.cc
index 1756c29..1a90847 100644
--- a/base/memory/shared_memory_posix.cc
+++ b/base/memory/shared_memory_posix.cc
@@ -279,9 +279,6 @@ bool SharedMemory::MapAt(off_t offset, size_t bytes) {
   if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
     return false;
 
-  if (memory_)
-    return false;
-
 #if defined(OS_ANDROID)
   // On Android, Map can be called with a size and offset of zero to use the
   // ashmem-determined size.
diff --git a/base/memory/shared_memory_unittest.cc b/base/memory/shared_memory_unittest.cc
index f2a9e74..b8999f6 100644
--- a/base/memory/shared_memory_unittest.cc
+++ b/base/memory/shared_memory_unittest.cc
@@ -477,6 +477,7 @@ TEST(SharedMemoryTest, MapAt) {
 
   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));
 
@@ -496,19 +497,6 @@ TEST(SharedMemoryTest, MapAt) {
   }
 }
 
-TEST(SharedMemoryTest, MapTwice) {
-  const uint32 kDataSize = 1024;
-  SharedMemory memory;
-  bool rv = memory.CreateAndMapAnonymous(kDataSize);
-  EXPECT_TRUE(rv);
-
-  void* old_address = memory.memory();
-
-  rv = memory.Map(kDataSize);
-  EXPECT_FALSE(rv);
-  EXPECT_EQ(old_address, memory.memory());
-}
-
 #if defined(OS_POSIX)
 // Create a shared memory object, mmap it, and mprotect it to PROT_EXEC.
 TEST(SharedMemoryTest, AnonymousExecutable) {
diff --git a/base/memory/shared_memory_win.cc b/base/memory/shared_memory_win.cc
index cc177ab..c9d603e 100644
--- a/base/memory/shared_memory_win.cc
+++ b/base/memory/shared_memory_win.cc
@@ -164,9 +164,6 @@ bool SharedMemory::MapAt(off_t offset, size_t bytes) {
   if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
     return false;
 
-  if (memory_)
-    return false;
-
   memory_ = MapViewOfFile(mapped_file_,
                           read_only_ ? FILE_MAP_READ : FILE_MAP_READ |
                               FILE_MAP_WRITE,