Implement all resolution change policies for desktop and tab capture.

media/base/video_util.h

Index: media/base/video_util.h
diff --git a/media/base/video_util.h b/media/base/video_util.h
index 7798ebe016e1a996bf1d0b022fe98ebbc702d53f..04013bc64778b54b65c52830ff3dace09efaa521 100644
--- a/media/base/video_util.h
+++ b/media/base/video_util.h
@@ -84,6 +84,26 @@ MEDIA_EXPORT void RotatePlaneByPixels(
 MEDIA_EXPORT gfx::Rect ComputeLetterboxRegion(const gfx::Rect& bounds,
                                               const gfx::Size& content);
 
+// Return a scaled |size| whose area is less than or equal to |target|, where
+// one of its dimensions is equal to |target|'s.  The aspect ratio of the result
+// is preserved as closely as possible.  If |size| is empty, its aspect ratio

[Wez, 2015/05/13 19:05:09]

nit: Aspect ratio of |size| is preserved as closely as possible.

[miu, 2015/05/14 01:21:33]

Done.

+// would be undefined; and in this case an empty Size would be returned.
+MEDIA_EXPORT gfx::Size ScaleSizeToFitWithinTarget(const gfx::Size& size,
+                                                  const gfx::Size& target);
+
+// Return a scaled |size| whose area is greater than or equal to |target|, where
+// one of its dimensions is equal to |target|'s.  The aspect ratio of the result
+// is preserved as closely as possible.  If |size| is empty, its aspect ratio

[Wez, 2015/05/13 19:05:09]

nit: You mean the aspect ratio of |size| is preserved.

[miu, 2015/05/14 01:21:33]

Done.

+// would be undefined; and in this case an empty Size would be returned.

[Wez, 2015/05/13 19:05:09]

I'd suggest just saying that the result is always empty if |size| is empty, here
and above.

[miu, 2015/05/14 01:21:33]

Done.

+MEDIA_EXPORT gfx::Size ScaleSizeToEncompassTarget(const gfx::Size& size,
+                                                  const gfx::Size& target);
+
+// Returns |size| with one of its dimensions increased such that the result
+// matches the aspect ratio of |target|.  If |target| is empty, its aspect ratio

[Wez, 2015/05/13 19:05:09]

It's not immediately obvious how this differs from ScaleSizeToEncompassTarget()
- is the difference that this function won't down-size if |size| is already
larger than |target| in both dimensions?

[miu, 2015/05/14 01:21:33]

Done.  Elaborated further in the comment.

+// would be undefined; and in this case an empty Size would be returned.

[Wez, 2015/05/13 19:05:09]

Surely the same is true if |size| is empty?

Suggest saying that if either of |size| or |target| are empty then the result
will be empty.

nit: Here and above, would it make more sense to CHECK() that these parameters
are not empty, since empty typically means that callers are doing the wrong
thing?

[miu, 2015/05/14 01:21:33]

Yes.
Done.
Perhaps.  A quick look-up shows there are 14+ callers of
ComputeLetterboxRegion().  I'm not sure if there are assumptions being made that
an empty input is valid and should produce an empty result.  I took a look at
the new functions, and the default behavior is actually reasonable in some
cases.  For example, when we call ScaleToEncompassTarget() with an empty target,
it makes logical sense that the result should also be an empty Size.

As these are shared media utility functions, I'll discuss this with Dale, and
follow-up in a later change if the CHECK() strategy is more appropriate.

+MEDIA_EXPORT gfx::Size PadToMatchAspectRatio(const gfx::Size& size,
+                                             const gfx::Size& target);
+
 // Copy an RGB bitmap into the specified |region_in_frame| of a YUV video frame.
 // Fills the regions outside |region_in_frame| with black.
 MEDIA_EXPORT void CopyRGBToVideoFrame(const uint8* source,