ScopedBufferLock: clarify check for contiguousness

This change makes ScopedBufferLock more readable by replacing the
confusingly named UnlockedNoncontiguousBuffer() with IsContiguous(),
and instead unlocking the 2D buffer as part of the fallback to
LockSlow() if the 2D buffer is noncontiguous.

Change-Id: I446de78823c99422e9a2a2675a4ddb2dce7ec0d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2268592Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Jesse McKenna <jessemckenna@google.com>
Cr-Commit-Position: refs/heads/master@{#783100}

media/capture/video/win/video_capture_device_mf_win.cc

@@ -129,33 +129,32 @@ class MFPhotoCallback final
 // and automatically unlocks the buffer when destroyed.
 class ScopedBufferLock {
  public:
-  ScopedBufferLock(ComPtr<IMFMediaBuffer> buffer) : buffer_(std::move(buffer)) {
+  explicit ScopedBufferLock(ComPtr<IMFMediaBuffer> buffer)
+      : buffer_(std::move(buffer)) {
     if (FAILED(buffer_.As(&buffer_2d_))) {
       LockSlow();
       return;
     }
     // Try lock methods from fastest to slowest: Lock2DSize(), then Lock2D(),
     // then finally LockSlow().
-    if ((Lock2DSize() || Lock2D()) && !UnlockedNoncontiguousBuffer())
-      return;
+    if (Lock2DSize() || Lock2D()) {
+      if (IsContiguous())
+        return;
+      buffer_2d_->Unlock2D();
+    }
     // Fall back to LockSlow() if 2D buffer was unsupported or noncontiguous.
     buffer_2d_ = nullptr;
     LockSlow();
   }
 
-  // Unlocks |buffer_2d_| and returns true if |buffer_2d_| is non-contiguous or
-  // has negative pitch. If |buffer_2d_| is contiguous with positive pitch,
-  // i.e., the buffer format that the surrounding code expects, returns false.
-  bool UnlockedNoncontiguousBuffer() {
+  // Returns whether |buffer_2d_| is contiguous with positive pitch, i.e., the
+  // buffer format that the surrounding code expects.
+  bool IsContiguous() {
     BOOL is_contiguous;
-    if (pitch_ > 0 &&
-        SUCCEEDED(buffer_2d_->IsContiguousFormat(&is_contiguous)) &&
-        is_contiguous &&
-        (length_ || SUCCEEDED(buffer_2d_->GetContiguousLength(&length_)))) {
-      return false;
-    }
-    buffer_2d_->Unlock2D();
-    return true;
+    return pitch_ > 0 &&
+           SUCCEEDED(buffer_2d_->IsContiguousFormat(&is_contiguous)) &&
+           is_contiguous &&
+           (length_ || SUCCEEDED(buffer_2d_->GetContiguousLength(&length_)));
   }
 
   bool Lock2DSize() {