Clear fast_ink GpuMemoryBuffer

The buffer contents may be uninitialized on some platforms. Ensure that
it is cleared before being displayed.

Change-Id: I55007e0728852d38911515019a2a7a3640ef613c
Bug: b:168735625
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2413179
Commit-Queue: Drew Davenport <ddavenport@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813182}

ash/fast_ink/fast_ink_host.cc

@@ -10,6 +10,7 @@
 
 #include <memory>
 
+#include "ash/public/cpp/ash_switches.h"
 #include "base/bind.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/base/math_util.h"
@@ -257,6 +258,21 @@ FastInkHost::FastInkHost(aura::Window* host_window,
                                   gpu::kNullSurfaceHandle);
   LOG_IF(ERROR, !gpu_memory_buffer_) << "Failed to create GPU memory buffer";
 
+  if (ash::switches::ShouldClearFastInkBuffer()) {
+    bool map_result = gpu_memory_buffer_->Map();
+    LOG_IF(ERROR, !map_result) << "Failed to map gpu buffer";
+    uint8_t* memory = static_cast<uint8_t*>(gpu_memory_buffer_->memory(0));
+    if (memory != nullptr) {
+      gfx::Size size = gpu_memory_buffer_->GetSize();
+      int stride = gpu_memory_buffer_->stride(0);
+      // Clear the buffer before usage, since it may be uninitialized.
+      // (http://b/168735625)
+      for (int i = 0; i < size.height(); ++i)
+        memset(memory + i * stride, 0, size.width() * 4);
+    }
+    gpu_memory_buffer_->Unmap();
+  }
+
   frame_sink_holder_ = std::make_unique<LayerTreeFrameSinkHolder>(
       this, host_window_->CreateLayerTreeFrameSink());
 }

ash/public/cpp/ash_switches.cc

@@ -20,6 +20,10 @@ constexpr base::TimeDelta kAshContextualNudgesMaxInterval =
 namespace ash {
 namespace switches {
 
+// Clear the fast ink buffer upon creation. This is needed on some devices that
+// do not zero out new buffers.
+const char kAshClearFastInkBuffer[] = "ash-clear-fast-ink-buffer";
+
 // Force the pointer (cursor) position to be kept inside root windows.
 const char kAshConstrainPointerToRoot[] = "ash-constrain-pointer-to-root";
 
@@ -166,5 +170,10 @@ bool IsUsingShelfAutoDim() {
   return base::CommandLine::ForCurrentProcess()->HasSwitch(kEnableDimShelf);
 }
 
+bool ShouldClearFastInkBuffer() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      kAshClearFastInkBuffer);
+}
+
 }  // namespace switches
 }  // namespace ash

ash/public/cpp/ash_switches.h

@@ -18,6 +18,7 @@ namespace switches {
 
 // Please keep alphabetized.
 // TODO(sky): fix order!
+ASH_PUBLIC_EXPORT extern const char kAshClearFastInkBuffer[];
 ASH_PUBLIC_EXPORT extern const char kAshConstrainPointerToRoot[];
 ASH_PUBLIC_EXPORT extern const char kAshContextualNudgesInterval[];
 ASH_PUBLIC_EXPORT extern const char kAshContextualNudgesResetShownCount[];
@@ -50,6 +51,7 @@ ASH_PUBLIC_EXPORT extern const char kTouchscreenUsableWhileScreenOff[];
 ASH_PUBLIC_EXPORT base::Optional<base::TimeDelta> ContextualNudgesInterval();
 ASH_PUBLIC_EXPORT bool ContextualNudgesResetShownCount();
 ASH_PUBLIC_EXPORT bool IsUsingShelfAutoDim();
+ASH_PUBLIC_EXPORT bool ShouldClearFastInkBuffer();
 
 }  // namespace switches
 }  // namespace ash

chrome/browser/chromeos/login/chrome_restart_request.cc

@@ -152,6 +152,7 @@ void DeriveCommandLine(const GURL& start_url,
     ::switches::kDisableWebRtcHWDecoding,
     ::switches::kDisableWebRtcHWEncoding,
     ::switches::kOzonePlatform,
+    ash::switches::kAshClearFastInkBuffer,
     ash::switches::kAshEnableTabletMode,
     ash::switches::kAshEnableWaylandServer,
     ash::switches::kAshForceEnableStylusTools,