Change Clock::SetMaxTime() to be safe even in the presence of slow pipelines.

Before this CL the contract of SetMaxTime was unsatisfiable; a clock client
could check that the max_time it was about to set wasn't greater than Elapsed()
before calling SetMaxTime(), but between the time that check was done and the
DCHECK inside SetMaxTime, time could move forward!
After this CL, SetMaxTime() is allowed to move the media_time_ backward and set
the underflow_ bit if the pipeline is slow enough.

BUG=113037,chromium-os:26939
TEST=A Debug binary on an underpowered ARM crosbook with no audio device plays back correctly.


Review URL: http://codereview.chromium.org/9582017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@124739 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 4 insertions, 5 deletions

diff --git a/media/base/clock.cc b/media/base/clock.cc
index 2517d1d..e57d280 100644
--- a/media/base/clock.cc
+++ b/media/base/clock.cc
@@ -72,8 +72,9 @@ void Clock::SetMaxTime(base::TimeDelta max_time) {
   UpdateReferencePoints();
   max_time_ = ClampToValidTimeRange(max_time);
 
-  DCHECK(media_time_ <= max_time_);
-  underflow_ = false;
+  underflow_ = media_time_ > max_time_;
+  if (underflow_)
+    media_time_ = max_time_;
 }
 
 void Clock::SetDuration(base::TimeDelta duration) {
diff --git a/media/base/clock.h b/media/base/clock.h
index 2854cb8..a5dff4d 100644
--- a/media/base/clock.h
+++ b/media/base/clock.h
@@ -56,8 +56,7 @@ class MEDIA_EXPORT Clock {
   // set to 0 (before SetDuration() is called).
   void SetTime(base::TimeDelta current_time, base::TimeDelta max_time);
 
-  // Sets the |max_time| to be returned by a call to Elapsed(). |max_time| must
-  // be greater than or equal to the current Elapsed() time.
+  // Sets the |max_time| to be returned by a call to Elapsed().
   void SetMaxTime(base::TimeDelta max_time);
 
   // Returns the current elapsed media time. Returns 0 if SetDuration() has
diff --git a/media/base/pipeline.cc b/media/base/pipeline.cc
index 2a7ca39..9da3df1 100644
--- a/media/base/pipeline.cc
+++ b/media/base/pipeline.cc
@@ -467,7 +467,6 @@ void Pipeline::OnVideoTimeUpdate(base::TimeDelta max_time) {
     return;
 
   DCHECK(!waiting_for_clock_update_);
-  DCHECK(clock_->Elapsed() <= max_time);
   clock_->SetMaxTime(max_time);
 }