Make CFX_RenderDevice::StretchBitMask() take RetainPtrs by value

More consistently pass bitmaps around by value, with move semantics,
rather than by const-ref. Change related code in the call stack to do
the same.

Also change variable names to follow the style guide.

Change-Id: I7c634e8b12cb306d0dd4eb093fecd9ebaea869ce
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/115531
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

core/fpdfapi/render/cpdf_imagerenderer.cpp

diff --git a/core/fpdfapi/render/cpdf_imagerenderer.cpp b/core/fpdfapi/render/cpdf_imagerenderer.cpp
index 1d27796..ae8fff5 100644
--- a/core/fpdfapi/render/cpdf_imagerenderer.cpp
+++ b/core/fpdfapi/render/cpdf_imagerenderer.cpp
@@ -476,23 +476,20 @@
         CFX_FillRenderOptions::WindingOptions());
     return false;
   }
-  RetainPtr<CFX_DIBBase> pAlphaMask;
-  if (m_pDIBBase->IsMaskFormat())
-    pAlphaMask = m_pDIBBase;
-  else
-    pAlphaMask = m_pDIBBase->CloneAlphaMask();
 
+  RetainPtr<CFX_DIBBase> alpha_mask =
+      m_pDIBBase->IsMaskFormat() ? m_pDIBBase : m_pDIBBase->CloneAlphaMask();
   if (fabs(m_ImageMatrix.b) >= 0.5f || fabs(m_ImageMatrix.c) >= 0.5f) {
     int left;
     int top;
-    RetainPtr<CFX_DIBitmap> pTransformed =
-        pAlphaMask->TransformTo(m_ImageMatrix, &left, &top);
-    if (!pTransformed)
+    alpha_mask = alpha_mask->TransformTo(m_ImageMatrix, &left, &top);
+    if (!alpha_mask) {
       return true;
+    }
 
     const int bitmap_alpha = FXSYS_roundf(m_Alpha * 255);
     m_pRenderStatus->GetRenderDevice()->SetBitMask(
-        pTransformed, left, top,
+        std::move(alpha_mask), left, top,
         ArgbEncode(0xff, bitmap_alpha, bitmap_alpha, bitmap_alpha));
     return false;
   }
@@ -512,7 +509,7 @@
 
   const int bitmap_alpha = FXSYS_roundf(m_Alpha * 255);
   m_pRenderStatus->GetRenderDevice()->StretchBitMask(
-      pAlphaMask, left, top, dest_width, dest_height,
+      std::move(alpha_mask), left, top, dest_width, dest_height,
       ArgbEncode(0xff, bitmap_alpha, bitmap_alpha, bitmap_alpha));
   return false;
 }

core/fxge/cfx_renderdevice.cpp

diff --git a/core/fxge/cfx_renderdevice.cpp b/core/fxge/cfx_renderdevice.cpp
index fe7098a..a4aebb4 100644
--- a/core/fxge/cfx_renderdevice.cpp
+++ b/core/fxge/cfx_renderdevice.cpp
@@ -967,18 +967,18 @@
                                     BlendMode::kNormal);
 }
 
-bool CFX_RenderDevice::StretchBitMask(const RetainPtr<CFX_DIBBase>& pBitmap,
+bool CFX_RenderDevice::StretchBitMask(RetainPtr<CFX_DIBBase> bitmap,
                                       int left,
                                       int top,
                                       int dest_width,
                                       int dest_height,
                                       uint32_t color) {
-  return StretchBitMaskWithFlags(pBitmap, left, top, dest_width, dest_height,
-                                 color, FXDIB_ResampleOptions());
+  return StretchBitMaskWithFlags(std::move(bitmap), left, top, dest_width,
+                                 dest_height, color, FXDIB_ResampleOptions());
 }
 
 bool CFX_RenderDevice::StretchBitMaskWithFlags(
-    const RetainPtr<CFX_DIBBase>& pBitmap,
+    RetainPtr<CFX_DIBBase> bitmap,
     int left,
     int top,
     int dest_width,
@@ -988,7 +988,7 @@
   FX_RECT dest_rect(left, top, left + dest_width, top + dest_height);
   FX_RECT clip_box = m_ClipBox;
   clip_box.Intersect(dest_rect);
-  return m_pDeviceDriver->StretchDIBits(std::move(pBitmap), argb, left, top,
+  return m_pDeviceDriver->StretchDIBits(std::move(bitmap), argb, left, top,
                                         dest_width, dest_height, &clip_box,
                                         options, BlendMode::kNormal);
 }

core/fxge/cfx_renderdevice.h

diff --git a/core/fxge/cfx_renderdevice.h b/core/fxge/cfx_renderdevice.h
index 8a363ff..f69d5d4 100644
--- a/core/fxge/cfx_renderdevice.h
+++ b/core/fxge/cfx_renderdevice.h
@@ -120,13 +120,13 @@
                   int left,
                   int top,
                   uint32_t argb);
-  bool StretchBitMask(const RetainPtr<CFX_DIBBase>& pBitmap,
+  bool StretchBitMask(RetainPtr<CFX_DIBBase> bitmap,
                       int left,
                       int top,
                       int dest_width,
                       int dest_height,
                       uint32_t color);
-  bool StretchBitMaskWithFlags(const RetainPtr<CFX_DIBBase>& pBitmap,
+  bool StretchBitMaskWithFlags(RetainPtr<CFX_DIBBase> bitmap,
                                int left,
                                int top,
                                int dest_width,