Extract some logic from transport_dib into shared_memory.

This CL contains no intended behavior change.

Some of the logic in transport_dib_posix.cc made assumptions about the internal
structure of SharedMemoryHandle. I've moved that logic into
shared_memory_posix.cc.

BUG=466437

Review URL: https://codereview.chromium.org/1143243007

Cr-Commit-Position: refs/heads/master@{#332246}

base/memory/shared_memory.h

@@ -130,6 +130,12 @@ class BASE_EXPORT SharedMemory {
       bool clean_up_resources_on_destruction);
 #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);
+#endif  // defined(OS_POSIX) && !defined(OS_ANDROID)
+
   // Creates a shared memory object as described by the options struct.
   // Returns true on success and false on failure.
   bool Create(const SharedMemoryCreateOptions& options);

base/memory/shared_memory_posix.cc

@@ -269,6 +269,15 @@ bool SharedMemory::CreateAndMapAnonymous(size_t size) {
 }
 
 #if !defined(OS_ANDROID)
+// static
+int SharedMemory::GetSizeFromSharedMemoryHandle(
+    const SharedMemoryHandle& handle) {
+  struct stat st;
+  if (fstat(handle.fd, &st) != 0)
+    return -1;
+  return st.st_size;
+}
+
 // Chromium mostly only uses the unique/private shmem as specified by
 // "name == L"". The exception is in the StatsTable.
 // TODO(jrg): there is no way to "clean up" all unused named shmem if

ui/surface/transport_dib_posix.cc

@@ -51,7 +51,7 @@ TransportDIB* TransportDIB::CreateWithHandle(Handle handle) {
 
 // static
 bool TransportDIB::is_valid_handle(Handle dib) {
-  return dib.fd >= 0;
+  return base::SharedMemory::IsHandleValid(dib);
 }
 
 // static
@@ -66,7 +66,7 @@ bool TransportDIB::is_valid_id(Id id) {
 skia::PlatformCanvas* TransportDIB::GetPlatformCanvas(int w, int h) {
   if ((!memory() && !Map()) || !VerifyCanvasSize(w, h))
     return NULL;
-  return skia::CreatePlatformCanvas(w, h, true, 
+  return skia::CreatePlatformCanvas(w, h, true,
                                     reinterpret_cast<uint8_t*>(memory()),
                                     skia::RETURN_NULL_ON_FAILURE);
 }
@@ -82,13 +82,12 @@ bool TransportDIB::Map() {
   if (memory())
     return true;
 
-  struct stat st;
-  if ((fstat(shared_memory_.handle().fd, &st) != 0) ||
-      (!shared_memory_.Map(st.st_size))) {
+  int size = base::SharedMemory::GetSizeFromSharedMemoryHandle(
+      shared_memory_.handle());
+  if (size == -1 || !shared_memory_.Map(size))
     return false;
-  }
 
-  size_ = st.st_size;
+  size_ = size;
 #endif
   return true;
 }