Fix --disable-remote-core-animation path

Ensure ca_context_id be initialized to 0 (otherwise the browser will
attempt to use it).

TBR=zmo

Bug: 785599
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Idcc8b0e6922c9842ecc7462fe93788aa942793db
Reviewed-on: https://chromium-review.googlesource.com/779306Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518368}

gpu/ipc/service/image_transport_surface_delegate.h

@@ -40,12 +40,12 @@ struct GPU_EXPORT SwapBuffersCompleteParams {
   // the browser process.
   // https://crbug.com/604052
   // Only one of ca_context_id or io_surface may be non-0.
-  CAContextID ca_context_id;
-  bool fullscreen_low_power_ca_context_valid;
-  CAContextID fullscreen_low_power_ca_context_id;
+  CAContextID ca_context_id = 0;
+  bool fullscreen_low_power_ca_context_valid = false;
+  CAContextID fullscreen_low_power_ca_context_id = 0;
   gfx::ScopedRefCountedIOSurfaceMachPort io_surface;
   gfx::Size pixel_size;
-  float scale_factor;
+  float scale_factor = 1.f;
   gpu::TextureInUseResponses in_use_responses;
 #endif
   gfx::SwapResponse response;