Revert 243791 "Revert of https://codereview.chromium.org/128443002/"

trunk/src/content/shell/renderer/test_runner/WebTestProxy.cpp

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/shell/renderer/test_runner/WebTestProxy.h"
 
 #include <cctype>
 
 #include "content/shell/renderer/test_runner/AccessibilityController.h"
 #include "content/shell/renderer/test_runner/EventSender.h"
@@ skipping 591 matching lines @@
     BLINK_ASSERT(!m_isPainting);
     BLINK_ASSERT(canvas());
     m_isPainting = true;
 
     WebSize pageSizeInPixels = webWidget()->size();
     WebFrame* webFrame = webView()->mainFrame();
 
     int pageCount = webFrame->printBegin(pageSizeInPixels);
     int totalHeight = pageCount * (pageSizeInPixels.height + 1) - 1;
 
-    SkCanvas* testCanvas = skia::TryCreateBitmapCanvas(pageSizeInPixels.width, totalHeight, true);
+    SkCanvas* testCanvas = skia::TryCreateBitmapCanvas(pageSizeInPixels.width, totalHeight, false);
     if (testCanvas) {
         discardBackingStore();
         m_canvas.reset(testCanvas);
     } else {
         webFrame->printEnd();
         return;
     }
 
     webFrame->printPagesWithBoundaries(canvas(), pageSizeInPixels);
     webFrame->printEnd();
 
     m_isPainting = false;
 }
 
 SkCanvas* WebTestProxyBase::canvas()
 {
     if (m_canvas.get())
         return m_canvas.get();
     WebSize widgetSize = webWidget()->size();
     float deviceScaleFactor = webView()->deviceScaleFactor();
     int scaledWidth = static_cast<int>(ceil(static_cast<float>(widgetSize.width) * deviceScaleFactor));
     int scaledHeight = static_cast<int>(ceil(static_cast<float>(widgetSize.height) * deviceScaleFactor));
-    m_canvas.reset(skia::CreateBitmapCanvas(scaledWidth, scaledHeight, true));
+    // We're allocating the canvas to be non-opaque (third parameter), so we
+    // don't end up with uninitialized memory if a layout test doesn't damage
+    // the entire view.
+    m_canvas.reset(skia::CreateBitmapCanvas(scaledWidth, scaledHeight, false));
     return m_canvas.get();
 }
 
 // Paints the entire canvas a semi-transparent black (grayish). This is used
 // by the layout tests in fast/repaint. The alpha value matches upstream.
 void WebTestProxyBase::displayRepaintMask()
 {
     canvas()->drawARGB(167, 0, 0, 0);
 }
 
@@ skipping 712 matching lines @@
 
 void WebTestProxyBase::resetInputMethod()
 {
     // If a composition text exists, then we need to let the browser process
     // to cancel the input method's ongoing composition session.
     if (m_webWidget)
         m_webWidget->confirmComposition();
 }
 
 }