base: Minor improvement to interface of base::SharedMemory.

The previous declaration of GetSizeFromSharedMemoryHandle() was returning an int
and overloading the meaning of the return value. I changed the interface to
return a bool, and have a size_t output parameter.

BUG=

Review URL: https://codereview.chromium.org/1380173002

Cr-Commit-Position: refs/heads/master@{#351893}

4 files changed, 26 insertions, 15 deletions

diff --git a/base/memory/shared_memory.h b/base/memory/shared_memory.h
index 4503d00..1049dd1 100644
--- a/base/memory/shared_memory.h
+++ b/base/memory/shared_memory.h
@@ -124,9 +124,11 @@ class BASE_EXPORT SharedMemory {
 #endif
 
 #if defined(OS_POSIX) && !defined(OS_ANDROID)
-  // Returns the size of the shared memory region referred to by |handle|.
-  // Returns '-1' on a failure to determine the size.
-  static int GetSizeFromSharedMemoryHandle(const SharedMemoryHandle& handle);
+  // Gets the size of the shared memory region referred to by |handle|.
+  // Returns false on a failure to determine the size. On success, populates the
+  // output variable |size|.
+  static bool GetSizeFromSharedMemoryHandle(const SharedMemoryHandle& handle,
+                                            size_t* size);
 #endif  // defined(OS_POSIX) && !defined(OS_ANDROID)
 
   // Creates a shared memory object as described by the options struct.
diff --git a/base/memory/shared_memory_mac.cc b/base/memory/shared_memory_mac.cc
index ab53f01..9cec29f 100644
--- a/base/memory/shared_memory_mac.cc
+++ b/base/memory/shared_memory_mac.cc
@@ -169,12 +169,16 @@ bool SharedMemory::CreateAndMapAnonymous(size_t size) {
 }
 
 // static
-int SharedMemory::GetSizeFromSharedMemoryHandle(
-    const SharedMemoryHandle& handle) {
+bool SharedMemory::GetSizeFromSharedMemoryHandle(
+    const SharedMemoryHandle& handle,
+    size_t* size) {
   struct stat st;
-  if (fstat(GetFdFromSharedMemoryHandle(handle), &st) != 0)
-    return -1;
-  return st.st_size;
+  if (fstat(handle.GetFileDescriptor().fd, &st) != 0)
+    return false;
+  if (st.st_size < 0)
+    return false;
+  *size = st.st_size;
+  return true;
 }
 
 // Chromium mostly only uses the unique/private shmem as specified by
diff --git a/base/memory/shared_memory_posix.cc b/base/memory/shared_memory_posix.cc
index 2e66b34..6a7c1d5 100644
--- a/base/memory/shared_memory_posix.cc
+++ b/base/memory/shared_memory_posix.cc
@@ -177,12 +177,16 @@ bool SharedMemory::CreateAndMapAnonymous(size_t size) {
 
 #if !defined(OS_ANDROID)
 // static
-int SharedMemory::GetSizeFromSharedMemoryHandle(
-    const SharedMemoryHandle& handle) {
+bool SharedMemory::GetSizeFromSharedMemoryHandle(
+    const SharedMemoryHandle& handle,
+    size_t* size) {
   struct stat st;
   if (fstat(handle.fd, &st) != 0)
-    return -1;
-  return st.st_size;
+    return false;
+  if (st.st_size < 0)
+    return false;
+  *size = st.st_size;
+  return true;
 }
 
 // Chromium mostly only uses the unique/private shmem as specified by
diff --git a/ui/surface/transport_dib_posix.cc b/ui/surface/transport_dib_posix.cc
index 0a55dbd..25b2529 100644
--- a/ui/surface/transport_dib_posix.cc
+++ b/ui/surface/transport_dib_posix.cc
@@ -73,9 +73,10 @@ bool TransportDIB::Map() {
   if (memory())
     return true;
 
-  int size = base::SharedMemory::GetSizeFromSharedMemoryHandle(
-      shared_memory_.handle());
-  if (size == -1 || !shared_memory_.Map(size))
+  size_t size;
+  bool success = base::SharedMemory::GetSizeFromSharedMemoryHandle(
+      shared_memory_.handle(), &size);
+  if (!success || !shared_memory_.Map(size))
     return false;
 
   size_ = size;